Mapping | Rule Title | Description | Rationale |
---|---|---|---|
1.1.1.1 | Disable Mounting of cramfs |
To configure the system to prevent the cramfs
kernel module from being loaded, add the following line to the file /etc/modprobe.d/cramfs.conf :
install cramfs /bin/trueTo configure the system to prevent the cramfs from being used,
add the following line to file /etc/modprobe.d/cramfs.conf :
blacklist cramfsThis effectively prevents usage of this uncommon filesystem. The cramfs filesystem type is a compressed read-only Linux filesystem embedded in small footprint systems. A cramfs image can be used without having to first decompress the image. |
Removing support for unneeded filesystem types reduces the local attack surface of the server. |
1.1.1.2 | Disable Mounting of squashfs |
To configure the system to prevent the squashfs
kernel module from being loaded, add the following line to the file /etc/modprobe.d/squashfs.conf :
install squashfs /bin/trueTo configure the system to prevent the squashfs from being used,
add the following line to file /etc/modprobe.d/squashfs.conf :
blacklist squashfsThis effectively prevents usage of this uncommon filesystem. The squashfs filesystem type is a compressed read-only Linux filesystem embedded in small footprint systems (similar to cramfs). A squashfs image can be used without having to first decompress the image. |
Removing support for unneeded filesystem types reduces the local attack surface of the system. |
1.1.1.2 | Disable Mounting of freevxfs |
To configure the system to prevent the freevxfs
kernel module from being loaded, add the following line to the file /etc/modprobe.d/freevxfs.conf :
install freevxfs /bin/trueTo configure the system to prevent the freevxfs from being used,
add the following line to file /etc/modprobe.d/freevxfs.conf :
blacklist freevxfsThis effectively prevents usage of this uncommon filesystem. |
Linux kernel modules which implement filesystems that are not needed by the local system should be disabled. |
1.1.1.3 | Disable Mounting of jffs2 |
To configure the system to prevent the jffs2
kernel module from being loaded, add the following line to the file /etc/modprobe.d/jffs2.conf :
install jffs2 /bin/trueTo configure the system to prevent the jffs2 from being used,
add the following line to file /etc/modprobe.d/jffs2.conf :
blacklist jffs2This effectively prevents usage of this uncommon filesystem. |
Linux kernel modules which implement filesystems that are not needed by the local system should be disabled. |
1.1.1.3 | Disable Mounting of udf |
To configure the system to prevent the udf
kernel module from being loaded, add the following line to the file /etc/modprobe.d/udf.conf :
install udf /bin/trueTo configure the system to prevent the udf from being used,
add the following line to file /etc/modprobe.d/udf.conf :
blacklist udfThis effectively prevents usage of this uncommon filesystem. The udf filesystem type is the universal disk format used to implement the ISO/IEC 13346 and ECMA-167 specifications. This is an open vendor filesystem type for data storage on a broad range of media. This filesystem type is neccessary to support writing DVDs and newer optical disc formats. |
Removing support for unneeded filesystem types reduces the local attack surface of the system. |
1.1.1.4 | Disable Mounting of hfs |
To configure the system to prevent the hfs
kernel module from being loaded, add the following line to the file /etc/modprobe.d/hfs.conf :
install hfs /bin/trueTo configure the system to prevent the hfs from being used,
add the following line to file /etc/modprobe.d/hfs.conf :
blacklist hfsThis effectively prevents usage of this uncommon filesystem. |
Linux kernel modules which implement filesystems that are not needed by the local system should be disabled. |
1.1.1.5 | Disable Mounting of hfsplus |
To configure the system to prevent the hfsplus
kernel module from being loaded, add the following line to the file /etc/modprobe.d/hfsplus.conf :
install hfsplus /bin/trueTo configure the system to prevent the hfsplus from being used,
add the following line to file /etc/modprobe.d/hfsplus.conf :
blacklist hfsplusThis effectively prevents usage of this uncommon filesystem. |
Linux kernel modules which implement filesystems that are not needed by the local system should be disabled. |
1.1.2 | Ensure /tmp Located On Separate Partition | The /tmp directory is a world-writable directory used for temporary file storage. Ensure it has its own partition or logical volume at installation time, or migrate it using LVM. | The /tmp partition is used as temporary storage by many programs. Placing /tmp in its own partition enables the setting of more restrictive mount options, which can help protect programs which use it. |
1.1.3 | Add noexec Option to /tmp |
The noexec mount option can be used to prevent binaries
from being executed out of /tmp.
Add the noexec option to the fourth column of
/etc/fstab for the line which controls mounting of
/tmp .
|
Allowing users to execute binaries from world-writable directories such as /tmp should never be necessary in normal operation and can expose the system to potential compromise. |
1.1.4 | Add nodev Option to /tmp |
The nodev mount option can be used to prevent device files from
being created in /tmp. Legitimate character and block devices
should not exist within temporary directories like /tmp.
Add the nodev option to the fourth column of
/etc/fstab for the line which controls mounting of
/tmp .
|
The only legitimate location for device files is the /dev directory located on the root partition. The only exception to this is chroot jails. |
1.1.5 | Add nosuid Option to /tmp |
The nosuid mount option can be used to prevent
execution of setuid programs in /tmp. The SUID and SGID permissions
should not be required in these world-writable directories.
Add the nosuid option to the fourth column of
/etc/fstab for the line which controls mounting of
/tmp .
|
The presence of SUID and SGID executables should be tightly controlled. Users should not be able to execute SUID or SGID binaries from temporary storage partitions. |
1.1.7 | Add noexec Option to /dev/shm |
The noexec mount option can be used to prevent binaries
from being executed out of /dev/shm.
It can be dangerous to allow the execution of binaries
from world-writable temporary storage directories such as /dev/shm.
Add the noexec option to the fourth column of
/etc/fstab for the line which controls mounting of
/dev/shm .
|
Allowing users to execute binaries from world-writable directories such as /dev/shm can expose the system to potential compromise. |
1.1.8 | Add nodev Option to /dev/shm |
The nodev mount option can be used to prevent creation of device
files in /dev/shm. Legitimate character and block devices should
not exist within temporary directories like /dev/shm.
Add the nodev option to the fourth column of
/etc/fstab for the line which controls mounting of
/dev/shm .
|
The only legitimate location for device files is the /dev directory located on the root partition. The only exception to this is chroot jails. |
1.1.9 | Add nosuid Option to /dev/shm |
The nosuid mount option can be used to prevent execution
of setuid programs in /dev/shm. The SUID and SGID permissions should not
be required in these world-writable directories.
Add the nosuid option to the fourth column of
/etc/fstab for the line which controls mounting of
/dev/shm .
|
The presence of SUID and SGID executables should be tightly controlled. Users should not be able to execute SUID or SGID binaries from temporary storage partitions. |
1.1.10 | Ensure /var Located On Separate Partition | The /var directory is used by daemons and other system services to store frequently-changing data. Ensure that /var has its own partition or logical volume at installation time, or migrate it using LVM. | Ensuring that /var is mounted on its own partition enables the setting of more restrictive mount options. This helps protect system services such as daemons or other programs which use it. It is not uncommon for the /var directory to contain world-writable directories installed by other software packages. |
1.1.11 | Ensure /var/tmp Located On Separate Partition | The /var/tmp directory is a world-writable directory used for temporary file storage. Ensure it has its own partition or logical volume at installation time, or migrate it using LVM. | The /var/tmp partition is used as temporary storage by many programs. Placing /var/tmp in its own partition enables the setting of more restrictive mount options, which can help protect programs which use it. |
1.1.12 | Add noexec Option to /var/tmp |
The noexec mount option can be used to prevent binaries
from being executed out of /var/tmp.
Add the noexec option to the fourth column of
/etc/fstab for the line which controls mounting of
/var/tmp .
|
Allowing users to execute binaries from world-writable directories such as /var/tmp should never be necessary in normal operation and can expose the system to potential compromise. |
1.1.13 | Add nodev Option to /var/tmp |
The nodev mount option can be used to prevent device files from
being created in /var/tmp. Legitimate character and block devices
should not exist within temporary directories like /var/tmp.
Add the nodev option to the fourth column of
/etc/fstab for the line which controls mounting of
/var/tmp .
|
The only legitimate location for device files is the /dev directory located on the root partition. The only exception to this is chroot jails. |
1.1.14 | Add nosuid Option to /var/tmp |
The nosuid mount option can be used to prevent
execution of setuid programs in /var/tmp. The SUID and SGID permissions
should not be required in these world-writable directories.
Add the nosuid option to the fourth column of
/etc/fstab for the line which controls mounting of
/var/tmp .
|
The presence of SUID and SGID executables should be tightly controlled. Users should not be able to execute SUID or SGID binaries from temporary storage partitions. |
1.1.15 | Ensure /var/log Located On Separate Partition |
System logs are stored in the /var/log directory.
Ensure that /var/log has its own partition or logical
volume at installation time, or migrate it using LVM.
|
Placing /var/log in its own partition enables better separation between log files and other files in /var/. |
1.1.16 | Ensure /var/log/audit Located On Separate Partition |
Audit logs are stored in the /var/log/audit directory.
Ensure that /var/log/audit has its own partition or logical
volume at installation time, or migrate it using LVM.
Make absolutely certain that it is large enough to store all
audit logs that will be created by the auditing daemon.
|
Placing /var/log/audit in its own partition enables better separation between audit files and other files, and helps ensure that auditing cannot be halted due to the partition running out of space. |
1.1.17 | Ensure /home Located On Separate Partition | If user home directories will be stored locally, create a separate partition for /home at installation time (or migrate it later using LVM). If /home will be mounted from another system such as an NFS server, then creating a separate partition is not necessary at installation time, and the mountpoint can instead be configured later. | Ensuring that /home is mounted on its own partition enables the setting of more restrictive mount options, and also helps ensure that users cannot trivially fill partitions used for log or audit data storage. |
1.1.18 | Add nodev Option to /home |
The nodev mount option can be used to prevent device files from
being created in /home.
Legitimate character and block devices should exist only in
the /dev directory on the root partition or within chroot
jails built for system services.
Add the nodev option to the fourth column of
/etc/fstab for the line which controls mounting of
/home .
|
The only legitimate location for device files is the /dev directory located on the root partition. The only exception to this is chroot jails. |
1.1.19 | Add noexec Option to Removable Media Partitions |
The noexec mount option prevents the direct execution of binaries
on the mounted filesystem. Preventing the direct execution of binaries from
removable media (such as a USB key) provides a defense against malicious
software that may be present on such untrusted media.
Add the noexec option to the fourth column of
/etc/fstab for the line which controls mounting of
any removable media partitions.
|
Allowing users to execute binaries from removable media such as USB keys exposes the system to potential compromise. |
1.1.20 | Add nodev Option to Removable Media Partitions |
The nodev mount option prevents files from being
interpreted as character or block devices.
Legitimate character and block devices should exist only in
the /dev directory on the root partition or within chroot
jails built for system services.
Add the nodev option to the fourth column of
/etc/fstab for the line which controls mounting of
any removable media partitions.
|
The only legitimate location for device files is the /dev directory located on the root partition. An exception to this is chroot jails, and it is not advised to set nodev on partitions which contain their root filesystems. |
1.1.21 | Add nosuid Option to Removable Media Partitions |
The nosuid mount option prevents set-user-identifier (SUID)
and set-group-identifier (SGID) permissions from taking effect. These permissions
allow users to execute binaries with the same permissions as the owner and group
of the file respectively. Users should not be allowed to introduce SUID and SGID
files into the system via partitions mounted from removeable media.
Add the nosuid option to the fourth column of
/etc/fstab for the line which controls mounting of
any removable media partitions.
|
The presence of SUID and SGID executables should be tightly controlled. Allowing users to introduce SUID or SGID binaries from partitions mounted off of removable media would allow them to introduce their own highly-privileged programs. |
1.1.22 | Verify that All World-Writable Directories Have Sticky Bits Set |
When the so-called 'sticky bit' is set on a directory,
only the owner of a given file may remove that file from the
directory. Without the sticky bit, any user with write access to a
directory may remove any file in the directory. Setting the sticky
bit prevents users from removing each other's files. In cases where
there is no reason for a directory to be world-writable, a better
solution is to remove that permission rather than to set the sticky
bit. However, if a directory is used by a particular application,
consult that application's documentation instead of blindly
changing modes.
To set the sticky bit on a world-writable directory DIR, run the following command: $ sudo chmod +t DIR |
Failing to set the sticky bit on public directories allows unauthorized
users to delete files in the directory structure.
The only authorized public directories are those temporary directories supplied with the system, or those designed to be temporary file repositories. The setting is normally reserved for directories used by the system, by users for temporary file storage (such as /tmp), and for directories requiring global read/write access. |
1.1.23 | Disable the Automounter |
The autofs daemon mounts and unmounts filesystems, such as user
home directories shared via NFS, on demand. In addition, autofs can be used to handle
removable media, and the default configuration provides the cdrom device as /misc/cd.
However, this method of providing access to removable media is not common, so autofs
can almost always be disabled if NFS is not in use. Even if NFS is required, it may be
possible to configure filesystem mounts statically by editing /etc/fstab
rather than relying on the automounter.
The autofs service can be disabled with the following command:
$ sudo systemctl mask --now autofs.service |
Disabling the automounter permits the administrator to
statically control filesystem mounting through /etc/fstab.
Additionally, automatically mounting filesystems permits easy introduction of unknown devices, thereby facilitating malicious activity. |
1.1.24 | Disable Modprobe Loading of USB Storage Driver |
To prevent USB storage devices from being used, configure the kernel module loading system
to prevent automatic loading of the USB storage driver.
To configure the system to prevent the usb-storage
kernel module from being loaded, add the following line to the file /etc/modprobe.d/usb-storage.conf :
install usb-storage /bin/trueTo configure the system to prevent the usb-storage from being used,
add the following line to file /etc/modprobe.d/usb-storage.conf :
blacklist usb-storageThis will prevent the modprobe program from loading the usb-storage module, but will not prevent an administrator (or another program) from using the insmod program to load the module manually. |
USB storage devices such as thumb drives can be used to introduce malicious software. |
1.2.3 | Ensure gpgcheck Enabled In Main yum Configuration |
The gpgcheck option controls whether
RPM packages' signatures are always checked prior to installation.
To configure yum to check package signatures before installing
them, ensure the following line appears in /etc/yum.conf in
the [main] section:
gpgcheck=1 |
Changes to any software components can have significant effects on the
overall security of the operating system. This requirement ensures the
software has not been tampered with and that it has been provided by a
trusted vendor.
Accordingly, patches, service packs, device drivers, or operating system components must be signed with a certificate recognized and approved by the organization. Verifying the authenticity of the software prior to installation validates the integrity of the patch or upgrade received from a vendor. This ensures the software has not been tampered with and that it has been provided by a trusted vendor. Self-signed certificates are disallowed by this requirement. Certificates used to verify the software must be from an approved Certificate Authority (CA). |
1.2.3 | Ensure Red Hat GPG Key Installed |
To ensure the system can cryptographically verify base software packages
come from Red Hat (and to connect to the Red Hat Network to receive them),
the Red Hat GPG key must properly be installed. To install the Red Hat GPG
key, run:
$ sudo subscription-manager registerIf the system is not connected to the Internet or an RHN Satellite, then install the Red Hat GPG key from trusted media such as the Red Hat installation CD-ROM or DVD. Assuming the disc is mounted in /media/cdrom, use the following command as the root user to import it into the keyring: $ sudo rpm --import /media/cdrom/RPM-GPG-KEYAlternatively, the key may be pre-loaded during the RHEL installation. In such cases, the key can be installed by running the following command: sudo rpm --import /etc/pki/rpm-gpg/RPM-GPG-KEY-redhat-release |
Changes to software components can have significant effects on the overall security of the operating system. This requirement ensures the software has not been tampered with and that it has been provided by a trusted vendor. The Red Hat GPG key is necessary to cryptographically verify packages are from Red Hat. |
1.2.3 | Ensure gpgcheck Enabled for All yum Package Repositories |
To ensure signature checking is not disabled for
any repos, remove any lines from files in /etc/yum.repos.d of the form:
gpgcheck=0 |
Verifying the authenticity of the software prior to installation validates the integrity of the patch or upgrade received from a vendor. This ensures the software has not been tampered with and that it has been provided by a trusted vendor. Self-signed certificates are disallowed by this requirement. Certificates used to verify the software must be from an approved Certificate Authority (CA)." |
1.2.5 | Disable Red Hat Network Service (rhnsd) |
The Red Hat Network service automatically queries Red Hat Network
servers to determine whether there are any actions that should be executed,
such as package updates. This only occurs if the system was registered to an
RHN server or satellite and managed as such.
The rhnsd service can be disabled with the following command:
$ sudo systemctl mask --now rhnsd.service |
Although systems management and patching is extremely important to system security, management by a system outside the enterprise enclave is not desirable for some environments. However, if the system is being managed by RHN or RHN Satellite Server the rhnsd daemon can remain on. |
1.3.1 | Build and Test AIDE Database |
Run the following command to generate a new database:
$ sudo /usr/sbin/aide --initBy default, the database will be written to the file /var/lib/aide/aide.db.new.gz. Storing the database, the configuration file /etc/aide.conf, and the binary /usr/sbin/aide (or hashes of these files), in a secure location (such as on read-only media) provides additional assurance about their integrity. The newly-generated database can be installed as follows: $ sudo cp /var/lib/aide/aide.db.new.gz /var/lib/aide/aide.db.gzTo initiate a manual check, run the following command: $ sudo /usr/sbin/aide --checkIf this check produces any unexpected output, investigate. |
For AIDE to be effective, an initial database of "known-good" information about files must be captured and it should be able to be verified against the installed files. |
1.3.1 | Install AIDE |
The aide package can be installed with the following command:
$ sudo yum install aide |
The AIDE package must be installed if it is to be available for integrity checking. |
1.3.2 | Configure Periodic Execution of AIDE |
At a minimum, AIDE should be configured to run a weekly scan.
To implement a daily execution of AIDE at 4:05am using cron, add the following line to /etc/crontab:
05 4 * * * root /usr/sbin/aide --checkTo implement a weekly execution of AIDE at 4:05am using cron, add the following line to /etc/crontab: 05 4 * * 0 root /usr/sbin/aide --checkAIDE can be executed periodically through other means; this is merely one example. The usage of cron's special time codes, such as @daily and @weekly is acceptable. |
By default, AIDE does not install itself for periodic execution. Periodically
running AIDE is necessary to reveal unexpected changes in installed files.
Unauthorized changes to the baseline configuration could make the system vulnerable to various attacks or allow unauthorized access to the operating system. Changes to operating system configurations can have unintended side effects, some of which may be relevant to security. Detecting such changes and providing an automated response can help avoid unintended, negative consequences that could ultimately affect the security state of the operating system. The operating system's Information Management Officer (IMO)/Information System Security Officer (ISSO) and System Administrators (SAs) must be notified via email and/or monitoring system trap when there is an unauthorized modification of a configuration item. |
1.4.1 | Set the UEFI Boot Loader Password |
The grub2 boot loader should have a superuser account and password
protection enabled to protect boot-time settings.
Since plaintext passwords are a security risk, generate a hash for the password by running the following command: # grub2-setpasswordWhen prompted, enter the password that was selected. |
Password protection on the boot loader configuration ensures users with physical access cannot trivially alter important bootloader settings. These include which kernel to use, and whether to enter single-user mode. |
1.4.1 | Set Boot Loader Password in grub2 |
The grub2 boot loader should have a superuser account and password
protection enabled to protect boot-time settings.
Since plaintext passwords are a security risk, generate a hash for the password by running the following command: # grub2-setpasswordWhen prompted, enter the password that was selected. |
Password protection on the boot loader configuration ensures users with physical access cannot trivially alter important bootloader settings. These include which kernel to use, and whether to enter single-user mode. |
1.4.2 | Verify /boot/grub2/user.cfg Group Ownership |
The file /boot/grub2/user.cfg should be group-owned by the root
group to prevent reading or modification of the file.
To properly set the group owner of /boot/grub2/user.cfg , run the command:
$ sudo chgrp root /boot/grub2/user.cfg |
The root group is a highly-privileged group. Furthermore, the group-owner of this file should not have any access privileges anyway. Non-root users who read the boot parameters may be able to identify weaknesses in security upon boot and be able to exploit them. |
1.4.2 | Verify /boot/efi/EFI/redhat/user.cfg Group Ownership |
The file /boot/efi/EFI/redhat/user.cfg should be group-owned by the
root group to prevent reading or modification of the file.
To properly set the group owner of /boot/efi/EFI/redhat/user.cfg , run the command:
$ sudo chgrp root /boot/efi/EFI/redhat/user.cfg |
The root group is a highly-privileged group. Furthermore, the group-owner of this file should not have any access privileges anyway. Non-root users who read the boot parameters may be able to identify weaknesses in security upon boot and be able to exploit them. |
1.4.2 | Verify /boot/grub2/user.cfg User Ownership |
The file /boot/grub2/user.cfg should be owned by the root
user to prevent reading or modification of the file.
To properly set the owner of /boot/grub2/user.cfg , run the command:
$ sudo chown root /boot/grub2/user.cfg |
Only root should be able to modify important boot parameters. Also, non-root users who read the boot parameters may be able to identify weaknesses in security upon boot and be able to exploit them. |
1.4.2 | Verify the UEFI Boot Loader grub.cfg Group Ownership |
The file /boot/efi/EFI/redhat/grub.cfg should
be group-owned by the root group to prevent
destruction or modification of the file.
To properly set the group owner of /boot/efi/EFI/redhat/grub.cfg , run the command:
$ sudo chgrp root /boot/efi/EFI/redhat/grub.cfg |
The root group is a highly-privileged group. Furthermore, the group-owner of this file should not have any access privileges anyway. |
1.4.2 | Verify /boot/efi/EFI/redhat/user.cfg User Ownership |
The file /boot/efi/EFI/redhat/user.cfg should be owned by the root
user to prevent reading or modification of the file.
To properly set the owner of /boot/efi/EFI/redhat/user.cfg , run the command:
$ sudo chown root /boot/efi/EFI/redhat/user.cfg |
Only root should be able to modify important boot parameters. Also, non-root users who read the boot parameters may be able to identify weaknesses in security upon boot and be able to exploit them. |
1.4.2 | Verify /boot/grub2/user.cfg Permissions |
File permissions for /boot/grub2/user.cfg should be set to 600.
To properly set the permissions of /boot/grub2/user.cfg , run the command:
$ sudo chmod 600 /boot/grub2/user.cfg |
Proper permissions ensure that only the root user can read or modify important boot parameters. |
1.4.2 | Verify /boot/efi/EFI/redhat/user.cfg Permissions |
File permissions for /boot/efi/EFI/redhat/user.cfg should be set to 600.
To properly set the permissions of /boot/efi/EFI/redhat/user.cfg , run the command:
$ sudo chmod 600 /boot/efi/EFI/redhat/user.cfg |
Proper permissions ensure that only the root user can read or modify important boot parameters. |
1.4.2 | Verify /boot/grub2/grub.cfg User Ownership |
The file /boot/grub2/grub.cfg should
be owned by the root user to prevent destruction
or modification of the file.
To properly set the owner of /boot/grub2/grub.cfg , run the command:
$ sudo chown root /boot/grub2/grub.cfg |
Only root should be able to modify important boot parameters. |
1.4.2 | Verify the UEFI Boot Loader grub.cfg Permissions |
File permissions for /boot/efi/EFI/redhat/grub.cfg should be set to 700.
To properly set the permissions of /boot/efi/EFI/redhat/grub.cfg , run the command:
$ sudo chmod 700 /boot/efi/EFI/redhat/grub.cfg |
Proper permissions ensure that only the root user can modify important boot parameters. |
1.4.2 | Verify /boot/grub2/grub.cfg Group Ownership |
The file /boot/grub2/grub.cfg should
be group-owned by the root group to prevent
destruction or modification of the file.
To properly set the group owner of /boot/grub2/grub.cfg , run the command:
$ sudo chgrp root /boot/grub2/grub.cfg |
The root group is a highly-privileged group. Furthermore, the group-owner of this file should not have any access privileges anyway. |
1.4.2 | Verify /boot/grub2/grub.cfg Permissions |
File permissions for /boot/grub2/grub.cfg should be set to 600.
To properly set the permissions of /boot/grub2/grub.cfg , run the command:
$ sudo chmod 600 /boot/grub2/grub.cfg |
Proper permissions ensure that only the root user can modify important boot parameters. |
1.4.2 | Verify the UEFI Boot Loader grub.cfg User Ownership |
The file /boot/efi/EFI/redhat/grub.cfg should
be owned by the root user to prevent destruction
or modification of the file.
To properly set the owner of /boot/efi/EFI/redhat/grub.cfg , run the command:
$ sudo chown root /boot/efi/EFI/redhat/grub.cfg |
Only root should be able to modify important boot parameters. |
1.4.3 | Require Authentication for Emergency Systemd Target |
Emergency mode is intended as a system recovery
method, providing a single user root access to the system
during a failed boot sequence.
By default, Emergency mode is protected by requiring a password and is set in /usr/lib/systemd/system/emergency.service. |
This prevents attackers with physical access from trivially bypassing security on the machine and gaining root access. Such accesses are further prevented by configuring the bootloader password. |
1.4.3 | Require Authentication for Single User Mode |
Single-user mode is intended as a system recovery
method, providing a single user root access to the system by
providing a boot option at startup.
By default, single-user mode is protected by requiring a password and is set in /usr/lib/systemd/system/rescue.service. |
This prevents attackers with physical access from trivially bypassing security on the machine and gaining root access. Such accesses are further prevented by configuring the bootloader password. |
1.5.1 | Disable Core Dumps for SUID programs |
To set the runtime status of the fs.suid_dumpable kernel parameter, run the following command: $ sudo sysctl -w fs.suid_dumpable=0To make sure that the setting is persistent, add the following line to a file in the directory /etc/sysctl.d: fs.suid_dumpable = 0 |
The core dump of a setuid program is more likely to contain sensitive data, as the program itself runs with greater privileges than the user who initiated execution of the program. Disabling the ability for any setuid program to write a core file decreases the risk of unauthorized access of such data. |
1.5.1 | Disable Core Dumps for All Users |
To disable core dumps for all users, add the following line to
/etc/security/limits.conf, or to a file within the
/etc/security/limits.d/ directory:
* hard core 0 |
A core dump includes a memory image taken at the time the operating system terminates an application. The memory image could contain sensitive data and is generally useful only for developers trying to debug problems. |
1.5.1 | Disable core dump backtraces | The ProcessSizeMax option in [Coredump] section of /etc/systemd/coredump.conf specifies the maximum size in bytes of a core which will be processed. Core dumps exceeding this size may be stored, but the backtrace will not be generated. | A core dump includes a memory image taken at the time the operating system terminates an application. The memory image could contain sensitive data and is generally useful only for developers or system operators trying to debug problems. Enabling core dumps on production systems is not recommended, however there may be overriding operational requirements to enable advanced debuging. Permitting temporary enablement of core dumps during such situations should be reviewed through local needs and policy. |
1.5.1 | Disable storing core dump | The Storage option in [Coredump] section of /etc/systemd/coredump.conf can be set to none to disable storing core dumps permanently. | A core dump includes a memory image taken at the time the operating system terminates an application. The memory image could contain sensitive data and is generally useful only for developers or system operators trying to debug problems. Enabling core dumps on production systems is not recommended, however there may be overriding operational requirements to enable advanced debuging. Permitting temporary enablement of core dumps during such situations should be reviewed through local needs and policy. |
1.5.2 | Enable NX or XD Support in the BIOS | Reboot the system and enter the BIOS or Setup configuration menu. Navigate the BIOS configuration menu and make sure that the option is enabled. The setting may be located under a Security section. Look for Execute Disable (XD) on Intel-based systems and No Execute (NX) on AMD-based systems. | Computers with the ability to prevent this type of code execution frequently put an option in the BIOS that will allow users to turn the feature on or off at will. |
1.5.2 | Install PAE Kernel on Supported 32-bit x86 Systems |
Systems that are using the 64-bit x86 kernel package
do not need to install the kernel-PAE package because the 64-bit
x86 kernel already includes this support. However, if the system is
32-bit and also supports the PAE and NX features as
determined in the previous section, the kernel-PAE package should
be installed to enable XD or NX support.
The kernel-PAE package can be installed with the following command:
$ sudo yum install kernel-PAEThe installation process should also have configured the bootloader to load the new kernel at boot. Verify this after reboot and modify /etc/default/grub if necessary. |
On 32-bit systems that support the XD or NX bit, the vendor-supplied PAE kernel is required to enable either Execute Disable (XD) or No Execute (NX) support. |
1.5.2 | Enable ExecShield via sysctl | By default on Red Hat Enterprise Linux 7 64-bit systems, ExecShield is enabled and can only be disabled if the hardware does not support ExecShield or is disabled in /etc/default/grub. | ExecShield uses the segmentation feature on all x86 systems to prevent execution in memory higher than a certain address. It writes an address as a limit in the code segment descriptor, to control where code can be executed, on a per-process basis. When the kernel places a process's memory regions such as the stack and heap higher than this address, the hardware prevents execution in that address range. This is enabled by default on the latest Red Hat and Fedora systems if supported by the hardware. |
1.5.3 | Enable Randomized Layout of Virtual Address Space |
To set the runtime status of the kernel.randomize_va_space kernel parameter, run the following command: $ sudo sysctl -w kernel.randomize_va_space=2To make sure that the setting is persistent, add the following line to a file in the directory /etc/sysctl.d: kernel.randomize_va_space = 2 |
Address space layout randomization (ASLR) makes it more difficult for an attacker to predict the location of attack code they have introduced into a process's address space during an attempt at exploitation. Additionally, ASLR makes it more difficult for an attacker to know the location of existing code in order to re-purpose it using return oriented programming (ROP) techniques. |
1.5.4 | Package "prelink" Must not be Installed |
The prelink package can be removed with the following command:
$ sudo yum erase prelink |
The use of the prelink package can interfere with the operation of AIDE since it binaries. Prelinking can also increase damage caused by vulnerability in a common library like libc. |
1.5.4 | Disable Prelinking |
The prelinking feature changes binaries in an attempt to decrease their startup
time. In order to disable it, change or add the following line inside the file
/etc/sysconfig/prelink:
PRELINKING=noNext, run the following command to return binaries to a normal, non-prelinked state: $ sudo /usr/sbin/prelink -ua |
Because the prelinking feature changes binaries, it can interfere with the operation of certain software and/or modes such as AIDE, FIPS, etc. |
1.6.1.1 | Install libselinux Package |
The libselinux package can be installed with the following command:
$ sudo yum install libselinux |
Security-enhanced Linux is a feature of the Linux kernel and a number of utilities with enhanced security functionality designed to add mandatory access controls to Linux. The libselinux package contains the core library of the Security-enhanced Linux system. |
1.6.1.2 | Ensure SELinux Not Disabled in /etc/default/grub | SELinux can be disabled at boot time by an argument in /etc/default/grub. Remove any instances of selinux=0 from the kernel arguments in that file to prevent SELinux from being disabled at boot. | Disabling a major host protection feature, such as SELinux, at boot time prevents it from confining system services at boot time. Further, it increases the chances that it will remain off during system operation. |
1.6.1.3 | Configure SELinux Policy |
The SELinux targeted policy is appropriate for
general-purpose desktops and servers, as well as systems in many other roles.
To configure the system to use this policy, add or correct the following line
in /etc/selinux/config:
SELINUXTYPE=targetedOther policies, such as mls, provide additional security labeling and greater confinement but are not compatible with many general-purpose use cases. |
Setting the SELinux policy to targeted or a more specialized policy
ensures the system will confine processes that are likely to be
targeted for exploitation, such as network or system services.
Note: During the development or debugging of SELinux modules, it is common to temporarily place non-production systems in permissive mode. In such temporary cases, SELinux policies should be developed, and once work is completed, the system should be reconfigured to . |
1.6.1.4 1.6.1.5 |
Ensure SELinux State is Enforcing |
The SELinux state should be set to enforcing at
system boot time. In the file /etc/selinux/config, add or correct the
following line to configure the system to boot into enforcing mode:
SELINUX=enforcing |
Setting the SELinux state to enforcing ensures SELinux is able to confine potentially compromised processes to the security policy, which is designed to prevent them from causing damage to the system or further elevating their privileges. |
1.6.1.6 | Ensure No Daemons are Unconfined by SELinux |
Daemons for which the SELinux policy does not contain rules will inherit the
context of the parent process. Because daemons are launched during
startup and descend from the init process, they inherit the unconfined_service_t context.
To check for unconfined daemons, run the following command: $ sudo ps -eZ | grep "unconfined_service_t"It should produce no output in a well-configured system. |
Daemons which run with the unconfined_service_t context may cause AVC denials, or allow privileges that the daemon does not require. |
1.6.1.7 | Uninstall setroubleshoot Package |
The SETroubleshoot service notifies desktop users of SELinux
denials. The service provides information around configuration errors,
unauthorized intrusions, and other potential errors.
The setroubleshoot package can be removed with the following command:
$ sudo yum erase setroubleshoot |
The SETroubleshoot service is an unnecessary daemon to have running on a server, especially if X Windows is removed or disabled. |
1.6.1.8 | Uninstall mcstrans Package |
The mcstransd daemon provides category label information
to client processes requesting information. The label translations are defined
in /etc/selinux/targeted/setrans.conf.
The mcstrans package can be removed with the following command:
$ sudo yum erase mcstrans |
Since this service is not used very often, disable it to reduce the amount of potentially vulnerable code running on the system. |
1.7.1 | Modify the System Message of the Day Banner |
To configure the system message banner edit /etc/motd. Replace the
default text with a message compliant with the local site policy or a legal
disclaimer.
The DoD required text is either:
You are accessing a U.S. Government (USG) Information System (IS) that is provided for USG-authorized use only. By using this IS (which includes any device attached to this IS), you consent to the following conditions: -The USG routinely intercepts and monitors communications on this IS for purposes including, but not limited to, penetration testing, COMSEC monitoring, network operations and defense, personnel misconduct (PM), law enforcement (LE), and counterintelligence (CI) investigations. -At any time, the USG may inspect and seize data stored on this IS. -Communications using, or data stored on, this IS are not private, are subject to routine monitoring, interception, and search, and may be disclosed or used for any USG-authorized purpose. -This IS includes security measures (e.g., authentication and access controls) to protect USG interests -- not for your personal benefit or privacy. -Notwithstanding the above, using this IS does not constitute consent to PM, LE or CI investigative searching or monitoring of the content of privileged communications, or work product, related to personal representation or services by attorneys, psychotherapists, or clergy, and their assistants. Such communications and work product are private and confidential. See User Agreement for details. OR: I've read & consent to terms in IS user agreem't. |
Display of a standardized and approved use notification before granting
access to the operating system ensures privacy and security notification
verbiage used is consistent with applicable federal laws, Executive Orders,
directives, policies, regulations, standards, and guidance.
System use notifications are required only for access via login interfaces with human users and are not required when such human interfaces do not exist. |
1.7.1.4 1.7.1.5 1.7.1.6 6.1.1 6.1.2 6.1.3 6.1.4 6.1.5 6.1.6 6.1.7 6.1.8 6.1.9 |
Verify and Correct File Permissions with RPM |
The RPM package management system can check file access permissions
of installed software packages, including many that are important
to system security.
Verify that the file permissions of system files
and commands match vendor values. Check the file permissions
with the following command:
$ sudo rpm -Va | awk '{ if (substr($0,2,1)=="M") print $NF }'Output indicates files that do not match vendor defaults. After locating a file with incorrect permissions, run the following command to determine which package owns it: $ rpm -qf FILENAME Next, run the following command to reset its permissions to the correct values: $ sudo rpm --setperms PACKAGENAME |
Permissions on system binaries and configuration files that are too generous could allow an unauthorized user to gain privileges that they should not have. The permissions set by the vendor should be maintained. Any deviations from this baseline should be investigated. |
1.7.1.4 1.7.1.5 1.7.1.6 6.1.1 6.1.2 6.1.3 6.1.4 6.1.5 6.1.6 6.1.7 6.1.8 6.1.9 |
Verify and Correct Ownership with RPM |
The RPM package management system can check file ownership
permissions of installed software packages, including many that are
important to system security. After locating a file with incorrect
permissions, which can be found with
rpm -Va | awk '{ if (substr($0,6,1)=="U" || substr($0,7,1)=="G") print $NF }'run the following command to determine which package owns it: $ rpm -qf FILENAMENext, run the following command to reset its permissions to the correct values: $ sudo rpm --setugids PACKAGENAME |
Ownership of binaries and configuration files that is incorrect could allow an unauthorized user to gain privileges that they should not have. The ownership set by the vendor should be maintained. Any deviations from this baseline should be investigated. |
1.7.2 | Modify the System Login Banner |
To configure the system login banner edit /etc/issue. Replace the
default text with a message compliant with the local site policy or a legal
disclaimer.
The DoD required text is either:
You are accessing a U.S. Government (USG) Information System (IS) that is provided for USG-authorized use only. By using this IS (which includes any device attached to this IS), you consent to the following conditions: -The USG routinely intercepts and monitors communications on this IS for purposes including, but not limited to, penetration testing, COMSEC monitoring, network operations and defense, personnel misconduct (PM), law enforcement (LE), and counterintelligence (CI) investigations. -At any time, the USG may inspect and seize data stored on this IS. -Communications using, or data stored on, this IS are not private, are subject to routine monitoring, interception, and search, and may be disclosed or used for any USG-authorized purpose. -This IS includes security measures (e.g., authentication and access controls) to protect USG interests -- not for your personal benefit or privacy. -Notwithstanding the above, using this IS does not constitute consent to PM, LE or CI investigative searching or monitoring of the content of privileged communications, or work product, related to personal representation or services by attorneys, psychotherapists, or clergy, and their assistants. Such communications and work product are private and confidential. See User Agreement for details. OR: I've read & consent to terms in IS user agreem't. |
Display of a standardized and approved use notification before granting
access to the operating system ensures privacy and security notification
verbiage used is consistent with applicable federal laws, Executive Orders,
directives, policies, regulations, standards, and guidance.
System use notifications are required only for access via login interfaces with human users and are not required when such human interfaces do not exist. |
1.7.2 | Make sure that the dconf databases are up-to-date with regards to respective keyfiles |
By default, DConf uses a binary database as a data backend.
The system-level database is compiled from keyfiles in the /etc/dconf/db/
directory by the dconf updatecommand. More specifically, content present in the following directories: /etc/dconf/db/gdm.d /etc/dconf/db/local.d |
Unlike text-based keyfiles, the binary database is impossible to check by OVAL. Therefore, in order to evaluate dconf configuration, both have to be true at the same time - configuration files have to be compliant, and the database needs to be more recent than those keyfiles, which gives confidence that it reflects them. |
1.7.3 | Modify the System Login Banner for Remote Connections |
To configure the system login banner edit /etc/issue.net. Replace the
default text with a message compliant with the local site policy or a legal
disclaimer.
The DoD required text is either:
You are accessing a U.S. Government (USG) Information System (IS) that is provided for USG-authorized use only. By using this IS (which includes any device attached to this IS), you consent to the following conditions: -The USG routinely intercepts and monitors communications on this IS for purposes including, but not limited to, penetration testing, COMSEC monitoring, network operations and defense, personnel misconduct (PM), law enforcement (LE), and counterintelligence (CI) investigations. -At any time, the USG may inspect and seize data stored on this IS. -Communications using, or data stored on, this IS are not private, are subject to routine monitoring, interception, and search, and may be disclosed or used for any USG-authorized purpose. -This IS includes security measures (e.g., authentication and access controls) to protect USG interests -- not for your personal benefit or privacy. -Notwithstanding the above, using this IS does not constitute consent to PM, LE or CI investigative searching or monitoring of the content of privileged communications, or work product, related to personal representation or services by attorneys, psychotherapists, or clergy, and their assistants. Such communications and work product are private and confidential. See User Agreement for details. OR: I've read & consent to terms in IS user agreem't. |
Display of a standardized and approved use notification before granting
access to the operating system ensures privacy and security notification
verbiage used is consistent with applicable federal laws, Executive Orders,
directives, policies, regulations, standards, and guidance.
System use notifications are required only for access via login interfaces with human users and are not required when such human interfaces do not exist. |
1.7.4 | Verify ownership of Message of the Day Banner |
To properly set the owner of /etc/motd , run the command:
$ sudo chown root /etc/motd |
Display of a standardized and approved use notification before granting
access to the operating system ensures privacy and security notification
verbiage used is consistent with applicable federal laws, Executive Orders,
directives, policies, regulations, standards, and guidance. Proper ownership will ensure that only root user can modify the banner. |
1.7.4 | Verify permissions on Message of the Day Banner |
To properly set the permissions of /etc/motd , run the command:
$ sudo chmod 0644 /etc/motd |
Display of a standardized and approved use notification before granting
access to the operating system ensures privacy and security notification
verbiage used is consistent with applicable federal laws, Executive Orders,
directives, policies, regulations, standards, and guidance. Proper permissions will ensure that only root user can modify the banner. |
1.7.4 | Verify Group Ownership of Message of the Day Banner |
To properly set the group owner of /etc/motd , run the command:
$ sudo chgrp root /etc/motd |
Display of a standardized and approved use notification before granting
access to the operating system ensures privacy and security notification
verbiage used is consistent with applicable federal laws, Executive Orders,
directives, policies, regulations, standards, and guidance. Proper group ownership will ensure that only root user can modify the banner. |
1.7.5 | Verify permissions on System Login Banner |
To properly set the permissions of /etc/issue , run the command:
$ sudo chmod 0644 /etc/issue |
Display of a standardized and approved use notification before granting
access to the operating system ensures privacy and security notification
verbiage used is consistent with applicable federal laws, Executive Orders,
directives, policies, regulations, standards, and guidance. Proper permissions will ensure that only root user can modify the banner. |
1.7.5 | Verify Group Ownership of System Login Banner |
To properly set the group owner of /etc/issue , run the command:
$ sudo chgrp root /etc/issue |
Display of a standardized and approved use notification before granting
access to the operating system ensures privacy and security notification
verbiage used is consistent with applicable federal laws, Executive Orders,
directives, policies, regulations, standards, and guidance. Proper group ownership will ensure that only root user can modify the banner. |
1.7.5 | Verify ownership of System Login Banner |
To properly set the owner of /etc/issue , run the command:
$ sudo chown root /etc/issue |
Display of a standardized and approved use notification before granting
access to the operating system ensures privacy and security notification
verbiage used is consistent with applicable federal laws, Executive Orders,
directives, policies, regulations, standards, and guidance. Proper ownership will ensure that only root user can modify the banner. |
1.7.6 | Verify Group Ownership of System Login Banner for Remote Connections |
To properly set the group owner of /etc/issue.net , run the command:
$ sudo chgrp root /etc/issue.net |
Display of a standardized and approved use notification before granting
access to the operating system ensures privacy and security notification
verbiage used is consistent with applicable federal laws, Executive Orders,
directives, policies, regulations, standards, and guidance. Proper group ownership will ensure that only root user can modify the banner. |
1.7.6 | Verify permissions on System Login Banner for Remote Connections |
To properly set the permissions of /etc/issue.net , run the command:
$ sudo chmod 0644 /etc/issue.net |
Display of a standardized and approved use notification before granting
access to the operating system ensures privacy and security notification
verbiage used is consistent with applicable federal laws, Executive Orders,
directives, policies, regulations, standards, and guidance. Proper permissions will ensure that only root user can modify the banner. |
1.7.6 | Verify ownership of System Login Banner for Remote Connections |
To properly set the owner of /etc/issue.net , run the command:
$ sudo chown root /etc/issue.net |
Display of a standardized and approved use notification before granting
access to the operating system ensures privacy and security notification
verbiage used is consistent with applicable federal laws, Executive Orders,
directives, policies, regulations, standards, and guidance. Proper ownership will ensure that only root user can modify the banner. |
1.8 | Ensure Software Patches Installed |
If the system is joined to the Red Hat Network, a Red Hat Satellite Server,
or a yum server, run the following command to install updates:
$ sudo yum updateIf the system is not configured to use one of these sources, updates (in the form of RPM packages) can be manually downloaded from the Red Hat Network and installed using rpm. NOTE: U.S. Defense systems are required to be patched within 30 days or sooner as local policy dictates. |
Installing software updates is a fundamental mitigation against the exploitation of publicly-known vulnerabilities. If the most recent security patches and updates are not installed, unauthorized users may take advantage of weaknesses in the unpatched software. The lack of prompt attention to patching could result in a system compromise. |
1.8.1 | Remove the GDM Package Group |
By removing the gdm package, the system no longer has GNOME installed
installed. If X Windows is not installed then the system cannot boot into graphical user mode.
This prevents the system from being accidentally or maliciously booted into a graphical.target
mode. To do so, run the following command:
$ sudo yum remove gdm |
Unnecessary service packages must not be installed to decrease the attack surface of the system. A graphical environment is unnecessary for certain types of systems including a virtualization hypervisor. |
1.8.2 | Set the GNOME3 Login Warning Banner Text |
In the default graphical environment, configuring the login warning banner text
in the GNOME Display Manager's login screen can be configured on the login
screen by setting banner-message-text to 'APPROVED_BANNER'
where APPROVED_BANNER is the approved banner for your environment.
To enable, add or edit banner-message-text to /etc/dconf/db/gdm.d/00-security-settings. For example: [org/gnome/login-screen] banner-message-text='APPROVED_BANNER'Once the setting has been added, add a lock to /etc/dconf/db/gdm.d/locks/00-security-settings-lock to prevent user modification. For example: /org/gnome/login-screen/banner-message-textAfter the settings have been set, run dconf update. When entering a warning banner that spans several lines, remember to begin and end the string with ' and use \n for new lines. |
An appropriate warning message reinforces policy awareness during the logon process and facilitates possible legal action against attackers. |
1.8.2 | Enable GNOME3 Login Warning Banner |
In the default graphical environment, displaying a login warning banner
in the GNOME Display Manager's login screen can be enabled on the login
screen by setting banner-message-enable to true.
To enable, add or edit banner-message-enable to /etc/dconf/db/gdm.d/00-security-settings. For example: [org/gnome/login-screen] banner-message-enable=trueOnce the setting has been added, add a lock to /etc/dconf/db/gdm.d/locks/00-security-settings-lock to prevent user modification. For example: /org/gnome/login-screen/banner-message-enableAfter the settings have been set, run dconf update. The banner text must also be set. |
Display of a standardized and approved use notification before granting access to the operating system
ensures privacy and security notification verbiage used is consistent with applicable federal laws,
Executive Orders, directives, policies, regulations, standards, and guidance.
For U.S. Government systems, system use notifications are required only for access via login interfaces with human users and are not required when such human interfaces do not exist. |
1.8.3 | Disable the GNOME3 Login User List |
In the default graphical environment, users logging directly into the
system are greeted with a login screen that displays all known users.
This functionality should be disabled by setting disable-user-list
to true.
To disable, add or edit disable-user-list to /etc/dconf/db/gdm.d/00-security-settings. For example: [org/gnome/login-screen] disable-user-list=trueOnce the setting has been added, add a lock to /etc/dconf/db/gdm.d/locks/00-security-settings-lock to prevent user modification. For example: /org/gnome/login-screen/disable-user-listAfter the settings have been set, run dconf update. |
Leaving the user list enabled is a security risk since it allows anyone with physical access to the system to quickly enumerate known user accounts without logging in. |
1.8.4 | Disable XDMCP in GDM |
XDMCP is an unencrypted protocol, and therefore, presents a security risk, see e.g.
XDMCP Gnome docs.
To disable XDMCP support in Gnome, set Enable to false under the [xdmcp] configuration section in /etc/gdm/custom.conf . For example:
[xdmcp] Enable=false |
XDMCP provides unencrypted remote access through the Gnome Display Manager (GDM) which does not provide for the confidentiality and integrity of user passwords or the remote session. If a privileged user were to login using XDMCP, the privileged user password could be compromised due to typed XEvents and keystrokes will traversing over the network in clear text. |
2.1.1 | Uninstall xinetd Package |
The xinetd package can be removed with the following command:
$ sudo yum erase xinetd |
Removing the xinetd package decreases the risk of the xinetd service's accidental (or intentional) activation. |
2.1.7 | Disable xinetd Service |
The xinetd service can be disabled with the following command:
$ sudo systemctl mask --now xinetd.service |
The xinetd service provides a dedicated listener service for some programs, which is no longer necessary for commonly-used network services. Disabling it ensures that these uncommon services are not running, and also prevents attacks against xinetd itself. |
2.2.1.1 | The Chrony package is installed |
System time should be synchronized between all systems in an environment. This is
typically done by establishing an authoritative time server or set of servers and having all
systems synchronize their clocks to them.
The chrony package can be installed with the following command:
$ sudo yum install chrony |
Time synchronization is important to support time sensitive security mechanisms like Kerberos and also ensures log files have consistent time records across the enterprise, which aids in forensic investigations. |
2.2.1.2 | A remote time server for Chrony is configured |
Chrony is a daemon which implements the Network Time Protocol (NTP). It is designed to
synchronize system clocks across a variety of systems and use a source that is highly
accurate. More information on chrony can be found at
http://chrony.tuxfamily.org/.
Chrony can be configured to be a client and/or a server.
Add or edit server or pool lines to /etc/chrony.conf as appropriate:
server <remote-server>Multiple servers may be configured. |
If chrony is in use on the system proper configuration is vital to ensuring time synchronization is working properly. |
2.2.1.2 | Ensure that chronyd is running under chrony user account | chrony is a daemon which implements the Network Time Protocol (NTP). It is designed to synchronize system clocks across a variety of systems and use a source that is highly accurate. More information on chrony can be found at http://chrony.tuxfamily.org/. Chrony can be configured to be a client and/or a server. To ensure that chronyd is running under chrony user account, remove any -u ... option from OPTIONS other than -u chrony, as chrony is run under its own user by default. This recommendation only applies if chrony is in use on the system. | If chrony is in use on the system proper configuration is vital to ensuring time synchronization is working properly. |
2.2.1.3 | Configure server restrictions for ntpd |
ntpd is a daemon which implements the Network Time Protocol (NTP). It is designed to
synchronize system clocks across a variety of systems and use a source that is highly
accurate. More information on NTP can be found at
http://www.ntp.org.
ntp can be configured to be a client and/or a server.
To ensure that ntpd implements correct server restrictions, make sure that the following lines exist in the file /etc/ntpd.conf:
restrict -4 default kod nomodify notrap nopeer noquery restrict -6 default kod nomodify notrap nopeer noqueryThis recommendation only applies if ntp is in use on the system. |
If ntp is in use on the system proper configuration is vital to ensuring time synchronization is working properly. |
2.2.1.3 | Enable the NTP Daemon |
The ntpd service can be enabled with the following command:
$ sudo systemctl enable ntpd.service |
Enabling the ntpd service ensures that the ntpd
service will be running and that the system will synchronize its time to
any servers specified. This is important whether the system is configured to be
a client (and synchronize only its own clock) or it is also acting as an NTP
server to other systems. Synchronizing time is essential for authentication
services such as Kerberos, but it is also important for maintaining accurate
logs and auditing possible security breaches.
The NTP daemon offers all of the functionality of ntpdate, which is now deprecated. |
2.2.1.3 | Configure ntpd To Run As ntp User |
ntp is a daemon which implements the Network Time Protocol (NTP). It is designed to
synchronize system clocks across a variety of systems and use a source that is highly
accurate. More information on NTP can be found at
http://www.ntp.org.
ntp can be configured to be a client and/or a server.
To ensure that ntpd is running as ntp user, Add or edit the
OPTIONS variable in /etc/sysconfig/ntpd to include ' -u ntp:ntp ':
OPTIONS="-u ntp:ntp"This recommendation only applies if ntp is in use on the system. |
If ntp is in use on the system proper configuration is vital to ensuring time synchronization is working properly. Running ntpd under dedicated user accounts limits the attack surface for potential attacker exploiting security flaws in the daemon or the protocol. |
2.2.1.3 | Specify a Remote NTP Server |
To specify a remote NTP server for time synchronization, edit
the file /etc/ntp.conf. Add or correct the following lines,
substituting the IP or hostname of a remote NTP server for ntpserver:
server ntpserverThis instructs the NTP software to contact that remote server to obtain time data. |
Synchronizing with an NTP server makes it possible to collate system logs from multiple sources or correlate computer events with real time events. |
2.2.1.3 | The Chronyd service is enabled | chrony is a daemon which implements the Network Time Protocol (NTP) is designed to synchronize system clocks across a variety of systems and use a source that is highly accurate. More information on chrony can be found at http://chrony.tuxfamily.org/. Chrony can be configured to be a client and/or a server. To enable Chronyd service, you can run: # systemctl enable chronyd.service This recommendation only applies if chrony is in use on the system. | If chrony is in use on the system proper configuration is vital to ensuring time synchronization is working properly. |
2.2.2 | Disable X Windows Startup By Setting Default Target |
Systems that do not require a graphical user interface should only boot by
default into multi-user.target mode. This prevents accidental booting of the system
into a graphical.target mode. Setting the system's default target to
multi-user.target will prevent automatic startup of the X server. To do so, run:
$ systemctl set-default multi-user.targetYou should see the following output: Removed symlink /etc/systemd/system/default.target. Created symlink from /etc/systemd/system/default.target to /usr/lib/systemd/system/multi-user.target. |
Services that are not required for system and application processes must not be active to decrease the attack surface of the system. X windows has a long history of security vulnerabilities and should not be used unless approved and documented. |
2.2.2 | Remove the X Windows Package Group |
By removing the xorg-x11-server-common package, the system no longer has X Windows
installed. If X Windows is not installed then the system cannot boot into graphical user mode.
This prevents the system from being accidentally or maliciously booted into a graphical.target
mode. To do so, run the following command:
$ sudo yum groupremove "X Window System" $ sudo yum remove xorg-x11-server-common |
Unnecessary service packages must not be installed to decrease the attack surface of the system. X windows has a long history of security vulnerabilities and should not be installed unless approved and documented. |
2.2.2 | Disable graphical user interface |
By removing the following packages, the system no longer has X Windows installed.
xorg-x11-server-Xorg xorg-x11-server-common xorg-x11-server-utils
If X Windows is not installed then the system cannot boot into graphical user mode.
This prevents the system from being accidentally or maliciously booted into a graphical.target
mode. To do so, run the following command:
sudo yum remove xorg-x11-server-Xorg xorg-x11-server-common xorg-x11-server-utils |
Unnecessary service packages must not be installed to decrease the attack surface of the system. X windows has a long history of security vulnerabilities and should not be installed unless approved and documented. |
2.2.3 | Disable Avahi Server Software |
The avahi-daemon service can be disabled with the following command:
$ sudo systemctl mask --now avahi-daemon.service |
Because the Avahi daemon service keeps an open network port, it is subject to network attacks. Its functionality is convenient but is only appropriate if the local network can be trusted. |
2.2.4 | Disable the CUPS Service |
The cups service can be disabled with the following command:
$ sudo systemctl mask --now cups.service |
Turn off unneeded services to reduce attack surface. |
2.2.4 | Uninstall CUPS Package |
The cups package can be removed with the following command:
$ sudo yum erase cups |
If the system does not need to print jobs or accept print jobs from other systems, it is recommended that CUPS be removed to reduce the potential attack surface. |
2.2.5 | Uninstall DHCP Server Package |
If the system does not need to act as a DHCP server,
the dhcp package can be uninstalled.
The dhcp package can be removed with the following command:
$ sudo yum erase dhcp |
Removing the DHCP server ensures that it cannot be easily or accidentally reactivated and disrupt network operation. |
2.2.5 | Disable DHCP Service |
The dhcpd service should be disabled on
any system that does not need to act as a DHCP server.
The dhcpd service can be disabled with the following command:
$ sudo systemctl mask --now dhcpd.service |
Unmanaged or unintentionally activated DHCP servers may provide faulty information to clients, interfering with the operation of a legitimate site DHCP server if there is one. |
2.2.6 | Uninstall openldap-servers Package | The openldap-servers package is not installed by default on a Red Hat Enterprise Linux 7 system. It is needed only by the OpenLDAP server, not by the clients which use LDAP for authentication. If the system is not intended for use as an LDAP Server it should be removed. | Unnecessary packages should not be installed to decrease the attack surface of the system. While this software is clearly essential on an LDAP server, it is not necessary on typical desktop or workstation systems. |
2.2.7 | Uninstall bind Package |
The named service is provided by the bind package.
The bind package can be removed with the following command:
$ sudo yum erase bind |
If there is no need to make DNS server software available, removing it provides a safeguard against its activation. |
2.2.7 | Disable Network File System (nfs) |
The Network File System (NFS) service allows remote hosts to mount
and interact with shared filesystems on the local system. If the local system
is not designated as a NFS server then this service should be disabled.
The nfs-server service can be disabled with the following command:
$ sudo systemctl mask --now nfs-server.service |
Unnecessary services should be disabled to decrease the attack surface of the system. |
2.2.8 | Uninstall vsftpd Package |
The vsftpd package can be removed with the following command: $ sudo yum erase vsftpd |
Removing the vsftpd package decreases the risk of its accidental activation. |
2.2.8 | Disable named Service |
The named service can be disabled with the following command:
$ sudo systemctl mask --now named.service |
All network services involve some risk of compromise due to implementation flaws and should be disabled if possible. |
2.2.9 | Disable vsftpd Service |
The vsftpd service can be disabled with the following command:
$ sudo systemctl mask --now vsftpd.service |
Running FTP server software provides a network-based avenue of attack, and should be disabled if not needed. Furthermore, the FTP protocol is unencrypted and creates a risk of compromising sensitive information. |
2.2.9 | Uninstall httpd Package |
The httpd package can be removed with the following command:
$ sudo yum erase httpd |
If there is no need to make the web server software available, removing it provides a safeguard against its activation. |
2.2.10 | Uninstall dovecot Package |
The dovecot package can be removed with the following command:
$ sudo yum erase dovecot |
If there is no need to make the Dovecot software available, removing it provides a safeguard against its activation. |
2.2.10 | Disable httpd Service |
The httpd service can be disabled with the following command:
$ sudo systemctl mask --now httpd.service |
Running web server software provides a network-based avenue of attack, and should be disabled if not needed. |
2.2.11 | Disable Dovecot Service |
The dovecot service can be disabled with the following command:
$ sudo systemctl mask --now dovecot.service |
Running an IMAP or POP3 server provides a network-based avenue of attack, and should be disabled if not needed. |
2.2.11 | Uninstall Samba Package |
The samba package can be removed with the following command: $ sudo yum erase samba |
If there is no need to make the Samba software available, removing it provides a safeguard against its activation. |
2.2.12 | Uninstall squid Package |
The squid package can be removed with the following command: $ sudo yum erase squid |
If there is no need to make the proxy server software available, removing it provides a safeguard against its activation. |
2.2.12 | Disable Samba |
The smb service can be disabled with the following command:
$ sudo systemctl mask --now smb.service |
Running a Samba server provides a network-based avenue of attack, and should be disabled if not needed. |
2.2.13 | Disable Squid |
The squid service can be disabled with the following command:
$ sudo systemctl mask --now squid.service |
Running proxy server software provides a network-based avenue of attack, and should be removed if not needed. |
2.2.13 | Uninstall net-snmp Package |
The net-snmp package provides the snmpd service.
The net-snmp package can be removed with the following command:
$ sudo yum erase net-snmp |
If there is no need to run SNMP server software, removing the package provides a safeguard against its activation. |
2.2.14 | Disable snmpd Service |
The snmpd service can be disabled with the following command:
$ sudo systemctl mask --now snmpd.service |
Running SNMP software provides a network-based avenue of attack, and should be disabled if not needed. |
2.2.14 | Uninstall ypserv Package |
The ypserv package can be removed with the following command:
$ sudo yum erase ypserv |
The NIS service provides an unencrypted authentication service which does not provide for the confidentiality and integrity of user passwords or the remote session. Removing the ypserv package decreases the risk of the accidental (or intentional) activation of NIS or NIS+ services. |
2.2.15 | Uninstall telnet-server Package |
The telnet-server package can be removed with the following command:
$ sudo yum erase telnet-server |
It is detrimental for operating systems to provide, or install by default,
functionality exceeding requirements or mission objectives. These
unnecessary capabilities are often overlooked and therefore may remain
unsecure. They increase the risk to the platform by providing additional
attack vectors.
The telnet service provides an unencrypted remote access service which does not provide for the confidentiality and integrity of user passwords or the remote session. If a privileged user were to login using this service, the privileged user password could be compromised. Removing the telnet-server package decreases the risk of the telnet service's accidental (or intentional) activation. |
2.2.16 | Disable Postfix Network Listening |
Edit the file /etc/postfix/main.cf to ensure that only the following
inet_interfaces line appears:
inet_interfaces = loopback-only |
This ensures postfix accepts mail messages (such as cron job reports) from the local system only, and not from the network, which protects it from network attack. |
2.2.17 | Disable rexec Service |
The rexec service, which is available with the rsh-server package
and runs as a service through xinetd or separately as a systemd socket, should be disabled.
If using xinetd, set disable to yes in /etc/xinetd.d/rexec.
The rexec socket can be disabled with the following command:
$ sudo systemctl mask --now rexec.socket |
The rexec service uses unencrypted network communications, which means that data from the login session, including passwords and all other information transmitted during the session, can be stolen by eavesdroppers on the network. |
2.2.17 | Disable rlogin Service |
The rlogin service, which is available with
the rsh-server package and runs as a service through xinetd or separately
as a systemd socket, should be disabled.
If using xinetd, set disable to yes in /etc/xinetd.d/rlogin.
The rlogin socket can be disabled with the following command:
$ sudo systemctl mask --now rlogin.socket |
The rlogin service uses unencrypted network communications, which means that data from the login session, including passwords and all other information transmitted during the session, can be stolen by eavesdroppers on the network. |
2.2.17 | Disable rsh Service |
The rsh service, which is available with
the rsh-server package and runs as a service through xinetd or separately
as a systemd socket, should be disabled.
If using xinetd, set disable to yes in /etc/xinetd.d/rsh.
The rsh socket can be disabled with the following command:
$ sudo systemctl mask --now rsh.socket |
The rsh service uses unencrypted network communications, which means that data from the login session, including passwords and all other information transmitted during the session, can be stolen by eavesdroppers on the network. |
2.2.17 | Uninstall nfs-utils Package |
The nfs-utils package can be removed with the following command:
$ sudo yum erase nfs-utils |
nfs-utils provides a daemon for the kernel NFS server and related tools. This package also contains the showmount program. showmount queries the mount daemon on a remote host for information about the Network File System (NFS) server on the remote host. For example, showmount can display the clients which are mounted on that host. |
2.2.18 | Uninstall rpcbind Package |
The rpcbind utility maps RPC services to the ports on which they listen.
RPC processes notify rpcbind when they start, registering the ports they
are listening on and the RPC program numbers they expect to serve. The
rpcbind service redirects the client to the proper port number so it can
communicate with the requested service. If the system does not require RPC
(such as for NFS servers) then this service should be disabled.
The rpcbind package can be removed with the following command:
$ sudo yum erase rpcbind |
If the system does not require rpc based services, it is recommended that rpcbind be disabled to reduce the attack surface. |
2.2.18 | Uninstall talk-server Package |
The talk-server package can be removed with the following command: $ sudo yum erase talk-server |
The talk software presents a security risk as it uses unencrypted protocols for communications. Removing the talk-server package decreases the risk of the accidental (or intentional) activation of talk services. |
2.2.18 | Disable rpcbind Service |
The rpcbind utility maps RPC services to the ports on which they listen.
RPC processes notify rpcbind when they start, registering the ports they
are listening on and the RPC program numbers they expect to serve. The
rpcbind service redirects the client to the proper port number so it can
communicate with the requested service. If the system does not require RPC
(such as for NFS servers) then this service should be disabled.
The rpcbind service can be disabled with the following command:
$ sudo systemctl mask --now rpcbind.service |
If the system does not require rpc based services, it is recommended that rpcbind be disabled to reduce the attack surface. |
2.2.19 | Ensure rsyncd service is disabled |
The rsyncd service can be disabled with the following command:
$ sudo systemctl mask --now rsyncd.service |
The rsyncd service presents a security risk as it uses unencrypted protocols for communication. |
2.2.19 | Disable telnet Service |
Make sure that the activation of the telnet service on system boot is disabled.
The telnet socket can be disabled with the following command:
$ sudo systemctl mask --now telnet.socket |
The telnet protocol uses unencrypted network communication, which means that data from the login session, including passwords and all other information transmitted during the session, can be stolen by eavesdroppers on the network. The telnet protocol is also subject to man-in-the-middle attacks. |
2.2.19 | Uninstall rsync Package |
The rsyncd service can be used to synchronize files between systems over network links.
The rsync package can be removed with the following command:
$ sudo yum erase rsync |
The rsyncd service presents a security risk as it uses unencrypted protocols for communication. |
2.2.20 | Disable tftp Service |
The tftp service should be disabled.
The tftp service can be disabled with the following command:
$ sudo systemctl mask --now tftp.service |
Disabling the tftp service ensures the system is not acting as a TFTP server, which does not provide encryption or authentication. |
2.3.1 | Remove NIS Client | The Network Information Service (NIS), formerly known as Yellow Pages, is a client-server directory service protocol used to distribute system configuration files. The NIS client (ypbind) was used to bind a system to an NIS server and receive the distributed configuration files. | The NIS service is inherently an insecure system that has been vulnerable to DOS attacks, buffer overflows and has poor authentication for querying NIS maps. NIS generally has been replaced by such protocols as Lightweight Directory Access Protocol (LDAP). It is recommended that the service be removed. |
2.3.2 | Uninstall rsh Package | The rsh package contains the client commands for the rsh services | These legacy clients contain numerous security exposures and have been replaced with the more secure SSH package. Even if the server is removed, it is best to ensure the clients are also removed to prevent users from inadvertently attempting to use these commands and therefore exposing their credentials. Note that removing the rsh package removes the clients for rsh,rcp, and rlogin. |
2.3.3 | Uninstall talk Package |
The talk package contains the client program for the
Internet talk protocol, which allows the user to chat with other users on
different systems. Talk is a communication program which copies lines from one
terminal to the terminal of another user.
The talk package can be removed with the following command:
$ sudo yum erase talk |
The talk software presents a security risk as it uses unencrypted protocols for communications. Removing the talk package decreases the risk of the accidental (or intentional) activation of talk client program. |
2.3.4 | Remove telnet Clients | The telnet client allows users to start connections to other systems via the telnet protocol. | The telnet protocol is insecure and unencrypted. The use of an unencrypted transmission medium could allow an unauthorized user to steal credentials. The ssh package provides an encrypted session and stronger security and is included in Red Hat Enterprise Linux 7. |
2.3.5 | Ensure LDAP client is not installed |
The Lightweight Directory Access Protocol (LDAP) is a service that provides
a method for looking up information from a central database.
The openldap-clients package can be removed with the following command:
$ sudo yum erase openldap-clients |
If the system does not need to act as an LDAP client, it is recommended that the software is removed to reduce the potential attack surface. |
3.1.2 | Deactivate Wireless Network Interfaces |
Deactivating wireless network interfaces should prevent normal usage of the wireless
capability.
Configure the system to disable all wireless network interfaces with the following command: $ sudo nmcli radio all off |
The use of wireless networking can introduce many different attack vectors into the organization's network. Common attack vectors such as malicious association and ad hoc networks will allow an attacker to spoof a wireless access point (AP), allowing validated systems to connect to the malicious AP and enabling the attacker to monitor and record network traffic. These malicious APs can also serve to create a man-in-the-middle attack or be used to create a denial of service to valid network resources. |
3.2.1 | Disable Kernel Parameter for IPv6 Forwarding |
To set the runtime status of the net.ipv6.conf.all.forwarding kernel parameter, run the following command: $ sudo sysctl -w net.ipv6.conf.all.forwarding=0To make sure that the setting is persistent, add the following line to a file in the directory /etc/sysctl.d: net.ipv6.conf.all.forwarding = 0 |
IP forwarding permits the kernel to forward packets from one network interface to another. The ability to forward packets between two networks is only appropriate for systems acting as routers. |
3.2.1 | Disable Kernel Parameter for IP Forwarding on IPv4 Interfaces |
To set the runtime status of the net.ipv4.ip_forward kernel parameter, run the following command: $ sudo sysctl -w net.ipv4.ip_forward=0To make sure that the setting is persistent, add the following line to a file in the directory /etc/sysctl.d: net.ipv4.ip_forward = 0 |
Routing protocol daemons are typically used on routers to exchange network topology information with other routers. If this capability is used when not required, system network information may be unnecessarily transmitted across the network. |
3.2.2 | Disable Kernel Parameter for Sending ICMP Redirects on all IPv4 Interfaces by Default |
To set the runtime status of the net.ipv4.conf.default.send_redirects kernel parameter, run the following command: $ sudo sysctl -w net.ipv4.conf.default.send_redirects=0To make sure that the setting is persistent, add the following line to a file in the directory /etc/sysctl.d: net.ipv4.conf.default.send_redirects = 0 |
ICMP redirect messages are used by routers to inform hosts that a more
direct route exists for a particular destination. These messages contain information
from the system's route table possibly revealing portions of the network topology.
The ability to send ICMP redirects is only appropriate for systems acting as routers. |
3.2.2 | Disable Kernel Parameter for Sending ICMP Redirects on all IPv4 Interfaces |
To set the runtime status of the net.ipv4.conf.all.send_redirects kernel parameter, run the following command: $ sudo sysctl -w net.ipv4.conf.all.send_redirects=0To make sure that the setting is persistent, add the following line to a file in the directory /etc/sysctl.d: net.ipv4.conf.all.send_redirects = 0 |
ICMP redirect messages are used by routers to inform hosts that a more
direct route exists for a particular destination. These messages contain information
from the system's route table possibly revealing portions of the network topology.
The ability to send ICMP redirects is only appropriate for systems acting as routers. |
3.3.1 | Disable Kernel Parameter for Accepting Source-Routed Packets on all IPv4 Interfaces |
To set the runtime status of the net.ipv4.conf.all.accept_source_route kernel parameter, run the following command: $ sudo sysctl -w net.ipv4.conf.all.accept_source_route=0To make sure that the setting is persistent, add the following line to a file in the directory /etc/sysctl.d: net.ipv4.conf.all.accept_source_route = 0 |
Source-routed packets allow the source of the packet to suggest routers
forward the packet along a different path than configured on the router,
which can be used to bypass network security measures. This requirement
applies only to the forwarding of source-routerd traffic, such as when IPv4
forwarding is enabled and the system is functioning as a router.
Accepting source-routed packets in the IPv4 protocol has few legitimate uses. It should be disabled unless it is absolutely required. |
3.3.1 | Disable Kernel Parameter for Accepting Source-Routed Packets on IPv4 Interfaces by Default |
To set the runtime status of the net.ipv4.conf.default.accept_source_route kernel parameter, run the following command: $ sudo sysctl -w net.ipv4.conf.default.accept_source_route=0To make sure that the setting is persistent, add the following line to a file in the directory /etc/sysctl.d: net.ipv4.conf.default.accept_source_route = 0 |
Source-routed packets allow the source of the packet to suggest routers
forward the packet along a different path than configured on the router,
which can be used to bypass network security measures.
Accepting source-routed packets in the IPv4 protocol has few legitimate uses. It should be disabled unless it is absolutely required, such as when IPv4 forwarding is enabled and the system is legitimately functioning as a router. |
3.3.1 | Disable Kernel Parameter for Accepting Source-Routed Packets on IPv6 Interfaces by Default |
To set the runtime status of the net.ipv6.conf.default.accept_source_route kernel parameter, run the following command: $ sudo sysctl -w net.ipv6.conf.default.accept_source_route=0To make sure that the setting is persistent, add the following line to a file in the directory /etc/sysctl.d: net.ipv6.conf.default.accept_source_route = 0 |
Source-routed packets allow the source of the packet to suggest routers forward the packet along a different path than configured on the router, which can be used to bypass network security measures. This requirement applies only to the forwarding of source-routerd traffic, such as when IPv6 forwarding is enabled and the system is functioning as a router. Accepting source-routed packets in the IPv6 protocol has few legitimate uses. It should be disabled unless it is absolutely required. |
3.3.1 | Disable Kernel Parameter for Accepting Source-Routed Packets on all IPv6 Interfaces |
To set the runtime status of the net.ipv6.conf.all.accept_source_route kernel parameter, run the following command: $ sudo sysctl -w net.ipv6.conf.all.accept_source_route=0To make sure that the setting is persistent, add the following line to a file in the directory /etc/sysctl.d: net.ipv6.conf.all.accept_source_route = 0 |
Source-routed packets allow the source of the packet to suggest routers
forward the packet along a different path than configured on the router, which can
be used to bypass network security measures. This requirement applies only to the
forwarding of source-routerd traffic, such as when IPv6 forwarding is enabled and
the system is functioning as a router.
Accepting source-routed packets in the IPv6 protocol has few legitimate uses. It should be disabled unless it is absolutely required. |
3.3.2 | Disable Accepting ICMP Redirects for All IPv4 Interfaces |
To set the runtime status of the net.ipv4.conf.all.accept_redirects kernel parameter, run the following command: $ sudo sysctl -w net.ipv4.conf.all.accept_redirects=0To make sure that the setting is persistent, add the following line to a file in the directory /etc/sysctl.d: net.ipv4.conf.all.accept_redirects = 0 |
ICMP redirect messages are used by routers to inform hosts that a more
direct route exists for a particular destination. These messages modify the
host's route table and are unauthenticated. An illicit ICMP redirect
message could result in a man-in-the-middle attack.
This feature of the IPv4 protocol has few legitimate uses. It should be disabled unless absolutely required." |
3.3.2 | Disable Kernel Parameter for Accepting ICMP Redirects by Default on IPv4 Interfaces |
To set the runtime status of the net.ipv4.conf.default.accept_redirects kernel parameter, run the following command: $ sudo sysctl -w net.ipv4.conf.default.accept_redirects=0To make sure that the setting is persistent, add the following line to a file in the directory /etc/sysctl.d: net.ipv4.conf.default.accept_redirects = 0 |
ICMP redirect messages are used by routers to inform hosts that a more
direct route exists for a particular destination. These messages modify the
host's route table and are unauthenticated. An illicit ICMP redirect
message could result in a man-in-the-middle attack.
This feature of the IPv4 protocol has few legitimate uses. It should be disabled unless absolutely required. |
3.3.2 | Disable Accepting ICMP Redirects for All IPv6 Interfaces |
To set the runtime status of the net.ipv6.conf.all.accept_redirects kernel parameter, run the following command: $ sudo sysctl -w net.ipv6.conf.all.accept_redirects=0To make sure that the setting is persistent, add the following line to a file in the directory /etc/sysctl.d: net.ipv6.conf.all.accept_redirects = 0 |
An illicit ICMP redirect message could result in a man-in-the-middle attack. |
3.3.2 | Disable Kernel Parameter for Accepting ICMP Redirects by Default on IPv6 Interfaces |
To set the runtime status of the net.ipv6.conf.default.accept_redirects kernel parameter, run the following command: $ sudo sysctl -w net.ipv6.conf.default.accept_redirects=0To make sure that the setting is persistent, add the following line to a file in the directory /etc/sysctl.d: net.ipv6.conf.default.accept_redirects = 0 |
An illicit ICMP redirect message could result in a man-in-the-middle attack. |
3.3.3 | Disable IPv6 Networking Support Automatic Loading |
To prevent the IPv6 kernel module (ipv6) from binding to the
IPv6 networking stack, add the following line to
/etc/modprobe.d/disabled.conf (or another file in
/etc/modprobe.d):
options ipv6 disable=1This permits the IPv6 module to be loaded (and thus satisfy other modules that depend on it), while disabling support for the IPv6 protocol. |
Any unnecessary network stacks - including IPv6 - should be disabled, to reduce the vulnerability to exploitation. |
3.3.3 | Configure Kernel Parameter for Accepting Secure Redirects By Default |
To set the runtime status of the net.ipv4.conf.default.secure_redirects kernel parameter, run the following command: $ sudo sysctl -w net.ipv4.conf.default.secure_redirects=0To make sure that the setting is persistent, add the following line to a file in the directory /etc/sysctl.d: net.ipv4.conf.default.secure_redirects = 0 |
Accepting "secure" ICMP redirects (from those gateways listed as default gateways) has few legitimate uses. It should be disabled unless it is absolutely required. |
3.3.3 | Disable Kernel Parameter for Accepting Secure ICMP Redirects on all IPv4 Interfaces |
To set the runtime status of the net.ipv4.conf.all.secure_redirects kernel parameter, run the following command: $ sudo sysctl -w net.ipv4.conf.all.secure_redirects=0To make sure that the setting is persistent, add the following line to a file in the directory /etc/sysctl.d: net.ipv4.conf.all.secure_redirects = 0 |
Accepting "secure" ICMP redirects (from those gateways listed as default gateways) has few legitimate uses. It should be disabled unless it is absolutely required. |
3.3.3 | Ensure IPv6 is disabled through kernel boot parameter |
To disable IPv6 protocol support in the Linux kernel,
add the argument ipv6.disable=1 to the default
GRUB2 command line for the Linux operating system.
To ensure that ipv6.disable=1 is added as a kernel command line
argument to newly installed kernels, add ipv6.disable=1 to the
default Grub2 command line for Linux operating systems. Modify the line within
/etc/default/grub as shown below:
GRUB_CMDLINE_LINUX="... ipv6.disable=1 ..."Run the following command to update command line for already installed kernels: # grubby --update-kernel=ALL --args="ipv6.disable=1" |
Any unnecessary network stacks, including IPv6, should be disabled to reduce the vulnerability to exploitation. |
3.3.4 | Enable Kernel Paremeter to Log Martian Packets on all IPv4 Interfaces by Default |
To set the runtime status of the net.ipv4.conf.default.log_martians kernel parameter, run the following command: $ sudo sysctl -w net.ipv4.conf.default.log_martians=1To make sure that the setting is persistent, add the following line to a file in the directory /etc/sysctl.d: net.ipv4.conf.default.log_martians = 1 |
The presence of "martian" packets (which have impossible addresses) as well as spoofed packets, source-routed packets, and redirects could be a sign of nefarious network activity. Logging these packets enables this activity to be detected. |
3.3.4 | Enable Kernel Parameter to Log Martian Packets on all IPv4 Interfaces |
To set the runtime status of the net.ipv4.conf.all.log_martians kernel parameter, run the following command: $ sudo sysctl -w net.ipv4.conf.all.log_martians=1To make sure that the setting is persistent, add the following line to a file in the directory /etc/sysctl.d: net.ipv4.conf.all.log_martians = 1 |
The presence of "martian" packets (which have impossible addresses) as well as spoofed packets, source-routed packets, and redirects could be a sign of nefarious network activity. Logging these packets enables this activity to be detected. |
3.3.5 | Enable Kernel Parameter to Ignore ICMP Broadcast Echo Requests on IPv4 Interfaces |
To set the runtime status of the net.ipv4.icmp_echo_ignore_broadcasts kernel parameter, run the following command: $ sudo sysctl -w net.ipv4.icmp_echo_ignore_broadcasts=1To make sure that the setting is persistent, add the following line to a file in the directory /etc/sysctl.d: net.ipv4.icmp_echo_ignore_broadcasts = 1 |
Responding to broadcast (ICMP) echoes facilitates network mapping
and provides a vector for amplification attacks.
Ignoring ICMP echo requests (pings) sent to broadcast or multicast addresses makes the system slightly more difficult to enumerate on the network. |
3.3.6 | Enable Kernel Parameter to Ignore Bogus ICMP Error Responses on IPv4 Interfaces |
To set the runtime status of the net.ipv4.icmp_ignore_bogus_error_responses kernel parameter, run the following command: $ sudo sysctl -w net.ipv4.icmp_ignore_bogus_error_responses=1To make sure that the setting is persistent, add the following line to a file in the directory /etc/sysctl.d: net.ipv4.icmp_ignore_bogus_error_responses = 1 |
Ignoring bogus ICMP error responses reduces log size, although some activity would not be logged. |
3.3.7 | Enable Kernel Parameter to Use Reverse Path Filtering on all IPv4 Interfaces by Default |
To set the runtime status of the net.ipv4.conf.default.rp_filter kernel parameter, run the following command: $ sudo sysctl -w net.ipv4.conf.default.rp_filter=1To make sure that the setting is persistent, add the following line to a file in the directory /etc/sysctl.d: net.ipv4.conf.default.rp_filter = 1 |
Enabling reverse path filtering drops packets with source addresses that should not have been able to be received on the interface they were received on. It should not be used on systems which are routers for complicated networks, but is helpful for end hosts and routers serving small networks. |
3.3.7 | Enable Kernel Parameter to Use Reverse Path Filtering on all IPv4 Interfaces |
To set the runtime status of the net.ipv4.conf.all.rp_filter kernel parameter, run the following command: $ sudo sysctl -w net.ipv4.conf.all.rp_filter=1To make sure that the setting is persistent, add the following line to a file in the directory /etc/sysctl.d: net.ipv4.conf.all.rp_filter = 1 |
Enabling reverse path filtering drops packets with source addresses that should not have been able to be received on the interface they were received on. It should not be used on systems which are routers for complicated networks, but is helpful for end hosts and routers serving small networks. |
3.3.8 | Enable Kernel Parameter to Use TCP Syncookies on Network Interfaces |
To set the runtime status of the net.ipv4.tcp_syncookies kernel parameter, run the following command: $ sudo sysctl -w net.ipv4.tcp_syncookies=1To make sure that the setting is persistent, add the following line to a file in the directory /etc/sysctl.d: net.ipv4.tcp_syncookies = 1 |
A TCP SYN flood attack can cause a denial of service by filling a system's TCP connection table with connections in the SYN_RCVD state. Syncookies can be used to track a connection when a subsequent ACK is received, verifying the initiator is attempting a valid connection and is not a flood source. This feature is activated when a flood condition is detected, and enables the system to continue servicing valid connection requests. |
3.3.9 | Disable Accepting Router Advertisements on all IPv6 Interfaces by Default |
To set the runtime status of the net.ipv6.conf.default.accept_ra kernel parameter, run the following command: $ sudo sysctl -w net.ipv6.conf.default.accept_ra=0To make sure that the setting is persistent, add the following line to a file in the directory /etc/sysctl.d: net.ipv6.conf.default.accept_ra = 0 |
An illicit router advertisement message could result in a man-in-the-middle attack. |
3.3.9 | Configure Accepting Router Advertisements on All IPv6 Interfaces |
To set the runtime status of the net.ipv6.conf.all.accept_ra kernel parameter, run the following command: $ sudo sysctl -w net.ipv6.conf.all.accept_ra=0To make sure that the setting is persistent, add the following line to a file in the directory /etc/sysctl.d: net.ipv6.conf.all.accept_ra = 0 |
An illicit router advertisement message could result in a man-in-the-middle attack. |
3.4.1 | Disable DCCP Support |
The Datagram Congestion Control Protocol (DCCP) is a
relatively new transport layer protocol, designed to support
streaming media and telephony.
To configure the system to prevent the dccp
kernel module from being loaded, add the following line to the file /etc/modprobe.d/dccp.conf :
install dccp /bin/trueTo configure the system to prevent the dccp from being used,
add the following line to file /etc/modprobe.d/dccp.conf :
blacklist dccp |
Disabling DCCP protects the system against exploitation of any flaws in its implementation. |
3.4.1 | Install tcp_wrappers Package |
When network services are using the xinetd service, the
tcp_wrappers package should be installed.
The tcp_wrappers package can be installed with the following command:
$ sudo yum install tcp_wrappers |
Access control methods provide the ability to enhance system security posture by restricting services and known good IP addresses and address ranges. This prevents connections from unknown hosts and protocols. |
3.4.2 | Disable SCTP Support |
The Stream Control Transmission Protocol (SCTP) is a
transport layer protocol, designed to support the idea of
message-oriented communication, with several streams of messages
within one connection.
To configure the system to prevent the sctp
kernel module from being loaded, add the following line to the file /etc/modprobe.d/sctp.conf :
install sctp /bin/trueTo configure the system to prevent the sctp from being used,
add the following line to file /etc/modprobe.d/sctp.conf :
blacklist sctp |
Disabling SCTP protects the system against exploitation of any flaws in its implementation. |
3.4.3 | Ensure /etc/hosts.deny is configured |
The file /etc/hosts.deny together with /etc/hosts.allow provides a
simple access control mechanism for network services supporting TCP wrappers.
The following line in the file ensures that access to services supporting this mechanism is denied to any clients
not mentioned in /etc/hosts.allow:
ALL: ALLIt is advised to inspect available network services which might be affected by modification of file mentioned above prior to performing the remediation of this rule. If there exist services which might be affected and access to them should not be blocked, modify the /etc/hosts.allow file appropriately before performing the remediation. |
Correct configuration in /etc/hosts.deny ensures that no explicitly mentioned clients will be able to connect to services supporting this access control mechanism. |
3.4.4 | Verify Group Ownership of /etc/hosts.allow |
To properly set the group owner of /etc/hosts.allow , run the command:
$ sudo chgrp root /etc/hosts.allow |
The /etc/hosts.allow file is used to control access of clients to daemons in the server. Insecure groupownership of this file could allow users to grant clients unrestricted access or no access at all to services in the server. |
3.4.4 | Verify Permissions on /etc/hosts.allow |
To properly set the permissions of /etc/hosts.allow , run the command:
$ sudo chmod 0644 /etc/hosts.allow |
The /etc/hosts.allow file is used to control access of clients to daemons in the server. Insecure groupownership of this file could allow users to grant clients unrestricted access or no access at all to services in the server. |
3.4.4 | Verify Ownership of /etc/hosts.allow |
To properly set the owner of /etc/hosts.allow , run the command:
$ sudo chown root /etc/hosts.allow |
The /etc/hosts.allow file is used to control access of clients to daemons in the server. Insecure groupownership of this file could allow users to grant clients unrestricted access or no access at all to services in the server. |
3.4.5 | Verify Group Ownership of /etc/hosts.deny |
To properly set the group owner of /etc/hosts.deny , run the command:
$ sudo chgrp root /etc/hosts.deny |
The /etc/hosts.deny file is used to control access of clients to daemons in the server. Insecure groupownership of this file could allow users to grant clients unrestricted access or no access at all to services in the server. |
3.4.5 | Verify Ownership of /etc/hosts.deny |
To properly set the owner of /etc/hosts.deny , run the command:
$ sudo chown root /etc/hosts.deny |
The /etc/hosts.deny file is used to control access of clients to daemons in the server. Insecure groupownership of this file could allow users to grant clients unrestricted access or no access at all to services in the server. |
3.4.5 | Verify Permissions on /etc/hosts.deny |
To properly set the permissions of /etc/hosts.deny , run the command:
$ sudo chmod 0644 /etc/hosts.deny |
The /etc/hosts.deny file is used to control access of clients to daemons in the server. Insecure groupownership of this file could allow users to grant clients unrestricted access or no access at all to services in the server. |
3.5.1.1 | Install firewalld Package |
The firewalld package can be installed with the following command:
$ sudo yum install firewalld |
"Firewalld" provides an easy and effective way to block/limit remote access to the system via ports, services, and protocols. Remote access services, such as those providing remote access to network devices and information systems, which lack automated control capabilities, increase risk and make remote user access management difficult at best. Remote access is access to DoD nonpublic information systems by an authorized user (or an information system) communicating through an external, non-organization-controlled network. Remote access methods include, for example, dial-up, broadband, and wireless. Red Hat Enterprise Linux 7 functionality (e.g., SSH) must be capable of taking enforcement action if the audit reveals unauthorized activity. Automated control of remote access sessions allows organizations to ensure ongoing compliance with remote access policies by enforcing connection rules of remote access applications on a variety of information system components (e.g., servers, workstations, notebook computers, smartphones, and tablets)." |
3.5.1.1 3.5.3.1.1 |
Install iptables Package |
The iptables package can be installed with the following command:
$ sudo yum install iptables |
iptables controls the Linux kernel network packet filtering code. iptables allows system operators to set up firewalls and IP masquerading, etc. |
3.5.1.4 | Verify firewalld Enabled |
The firewalld service can be enabled with the following command:
$ sudo systemctl enable firewalld.service |
Access control methods provide the ability to enhance system security posture by restricting services and known good IP addresses and address ranges. This prevents connections from unknown hosts and protocols. |
3.5.1.5 | Set Default firewalld Zone for Incoming Packets |
To set the default zone to drop for
the built-in default zone which processes incoming IPv4 and IPv6 packets,
modify the following line in
/etc/firewalld/firewalld.conf to be:
DefaultZone=drop |
In firewalld the default zone is applied only after all the applicable rules in the table are examined for a match. Setting the default zone to drop implements proper design for a firewall, i.e. any packets which are not explicitly permitted should not be accepted. |
3.5.3 | Disable RDS Support |
The Reliable Datagram Sockets (RDS) protocol is a transport
layer protocol designed to provide reliable high-bandwidth,
low-latency communications between nodes in a cluster.
To configure the system to prevent the rds
kernel module from being loaded, add the following line to the file /etc/modprobe.d/rds.conf :
install rds /bin/trueTo configure the system to prevent the rds from being used,
add the following line to file /etc/modprobe.d/rds.conf :
blacklist rds |
Disabling RDS protects the system against exploitation of any flaws in its implementation. |
3.5.3.2.6 | Verify iptables Enabled |
The iptables service can be enabled with the following command:
$ sudo systemctl enable iptables.service |
The iptables service provides the system's host-based firewalling capability for IPv4 and ICMP. |
3.5.3.3.6 | Verify ip6tables Enabled if Using IPv6 |
The ip6tables service can be enabled with the following command:
$ sudo systemctl enable ip6tables.service |
The ip6tables service provides the system's host-based firewalling capability for IPv6 and ICMPv6. |
3.5.4 | Disable TIPC Support |
The Transparent Inter-Process Communication (TIPC) protocol
is designed to provide communications between nodes in a
cluster.
To configure the system to prevent the tipc
kernel module from being loaded, add the following line to the file /etc/modprobe.d/tipc.conf :
install tipc /bin/trueTo configure the system to prevent the tipc from being used,
add the following line to file /etc/modprobe.d/tipc.conf :
blacklist tipc |
Disabling TIPC protects the system against exploitation of any flaws in its implementation. |
4.1.1.1 | Ensure the audit Subsystem is Installed | The audit package should be installed. | The auditd service is an access monitoring and accounting daemon, watching system calls to audit any access, in comparison with potential local access control policy such as SELinux policy. |
4.1.1.2 | Enable auditd Service |
The auditd service is an essential userspace component of
the Linux Auditing System, as it is responsible for writing audit records to
disk.
The auditd service can be enabled with the following command:
$ sudo systemctl enable auditd.service |
Without establishing what type of events occurred, it would be difficult
to establish, correlate, and investigate the events leading up to an outage or attack.
Ensuring the auditd service is active ensures audit records
generated by the kernel are appropriately recorded.
Additionally, a properly configured audit subsystem ensures that actions of individual system users can be uniquely traced to those users so they can be held accountable for their actions. |
4.1.1.3 | Enable Auditing for Processes Which Start Prior to the Audit Daemon |
To ensure all processes can be audited, even those which start
prior to the audit daemon, add the argument audit=1 to the default
GRUB 2 command line for the Linux operating system.
To ensure that audit=1 is added as a kernel command line
argument to newly installed kernels, add audit=1 to the
default Grub2 command line for Linux operating systems. Modify the line within
/etc/default/grub as shown below:
GRUB_CMDLINE_LINUX="... audit=1 ..."Run the following command to update command line for already installed kernels: # grubby --update-kernel=ALL --args="audit=1" |
Each process on the system carries an "auditable" flag which indicates whether its activities can be audited. Although auditd takes care of enabling this for all processes which launch after it does, adding the kernel argument ensures it is set for every process during boot. |
4.1.2.1 | Configure auditd Max Log File Size |
Determine the amount of audit data (in megabytes)
which should be retained in each log file. Edit the file
/etc/audit/auditd.conf. Add or modify the following line, substituting
the correct value of 6 for STOREMB:
max_log_file = STOREMBSet the value to 6 (MB) or higher for general-purpose systems. Larger values, of course, support retention of even more audit data. |
The total storage for audit log files must be large enough to retain log information over the period required. This is a function of the maximum log file size and the number of logs retained. |
4.1.2.2 | Configure auditd max_log_file_action Upon Reaching Maximum Log Size |
The default action to take when the logs reach their maximum size
is to rotate the log files, discarding the oldest one. To configure the action taken
by auditd, add or correct the line in /etc/audit/auditd.conf:
max_log_file_action = ACTIONPossible values for ACTION are described in the auditd.conf man page. These include:
|
Automatically rotating logs (by setting this to rotate) minimizes the chances of the system unexpectedly running out of disk space by being overwhelmed with log data. However, for systems that must never discard log data, or which use external processes to transfer it and reclaim space, keep_logs can be employed. |
4.1.2.3 | Configure auditd mail_acct Action on Low Disk Space |
The auditd service can be configured to send email to
a designated account in certain situations. Add or correct the following line
in /etc/audit/auditd.conf to ensure that administrators are notified
via email for those situations:
action_mail_acct = root |
Email sent to the root account is typically aliased to the administrators of the system, who can take appropriate action. |
4.1.2.3 | Configure auditd admin_space_left Action on Low Disk Space |
The auditd service can be configured to take an action
when disk space is running low but prior to running out of space completely.
Edit the file /etc/audit/auditd.conf. Add or modify the following line,
substituting ACTION appropriately:
admin_space_left_action = ACTIONSet this value to single to cause the system to switch to single user mode for corrective action. Acceptable values also include suspend and halt. For certain systems, the need for availability outweighs the need to log all actions, and a different setting should be determined. Details regarding all possible values for ACTION are described in the auditd.conf man page. |
Administrators should be made aware of an inability to record audit records. If a separate partition or logical volume of adequate size is used, running low on space for audit records should never occur. |
4.1.2.3 | Configure auditd space_left Action on Low Disk Space |
The auditd service can be configured to take an action
when disk space starts to run low.
Edit the file /etc/audit/auditd.conf. Modify the following line,
substituting ACTION appropriately:
space_left_action = ACTIONPossible values for ACTION are described in the auditd.conf man page. These include:
|
Notifying administrators of an impending disk space problem may allow them to take corrective action prior to any disruption. |
4.1.2.4 | Extend Audit Backlog Limit for the Audit Daemon |
To improve the kernel capacity to queue all log events, even those which occurred
prior to the audit daemon, add the argument audit_backlog_limit=8192 to the default
GRUB 2 command line for the Linux operating system.
To ensure that audit_backlog_limit=8192 is added as a kernel command line
argument to newly installed kernels, add audit_backlog_limit=8192 to the
default Grub2 command line for Linux operating systems. Modify the line within
/etc/default/grub as shown below:
GRUB_CMDLINE_LINUX="... audit_backlog_limit=8192 ..."Run the following command to update command line for already installed kernels: # grubby --update-kernel=ALL --args="audit_backlog_limit=8192" |
audit_backlog_limit sets the queue length for audit events awaiting transfer to the audit daemon. Until the audit daemon is up and running, all log messages are stored in this queue. If the queue is overrun during boot process, the action defined by audit failure flag is taken. |
4.1.3 | Record Attempts to Alter Time Through stime |
If the auditd daemon is configured to use the
augenrules program to read audit rules during daemon startup (the
default), add the following line to a file with suffix .rules in the
directory /etc/audit/rules.d for both 32 bit and 64 bit systems:
-a always,exit -F arch=b32 -S stime -F key=audit_time_rulesSince the 64 bit version of the "stime" system call is not defined in the audit lookup table, the corresponding "-F arch=b64" form of this rule is not expected to be defined on 64 bit systems (the aforementioned "-F arch=b32" stime rule form itself is sufficient for both 32 bit and 64 bit systems). If the auditd daemon is configured to use the auditctl utility to read audit rules during daemon startup, add the following line to /etc/audit/audit.rules file for both 32 bit and 64 bit systems: -a always,exit -F arch=b32 -S stime -F key=audit_time_rulesSince the 64 bit version of the "stime" system call is not defined in the audit lookup table, the corresponding "-F arch=b64" form of this rule is not expected to be defined on 64 bit systems (the aforementioned "-F arch=b32" stime rule form itself is sufficient for both 32 bit and 64 bit systems). The -k option allows for the specification of a key in string form that can be used for better reporting capability through ausearch and aureport. Multiple system calls can be defined on the same line to save space if desired, but is not required. See an example of multiple combined system calls: -a always,exit -F arch=b64 -S adjtimex,settimeofday -F key=audit_time_rules |
Arbitrary changes to the system time can be used to obfuscate nefarious activities in log files, as well as to confuse network services that are highly dependent upon an accurate system time (such as sshd). All changes to the system time should be audited. |
4.1.3 | Record attempts to alter time through settimeofday |
If the auditd daemon is configured to use the
augenrules program to read audit rules during daemon startup (the
default), add the following line to a file with suffix .rules in the
directory /etc/audit/rules.d:
-a always,exit -F arch=b32 -S settimeofday -F key=audit_time_rulesIf the system is 64 bit then also add the following line: -a always,exit -F arch=b64 -S settimeofday -F key=audit_time_rulesIf the auditd daemon is configured to use the auditctl utility to read audit rules during daemon startup, add the following line to /etc/audit/audit.rules file: -a always,exit -F arch=b32 -S settimeofday -F key=audit_time_rulesIf the system is 64 bit then also add the following line: -a always,exit -F arch=b64 -S settimeofday -F key=audit_time_rulesThe -k option allows for the specification of a key in string form that can be used for better reporting capability through ausearch and aureport. Multiple system calls can be defined on the same line to save space if desired, but is not required. See an example of multiple combined syscalls: -a always,exit -F arch=b64 -S adjtimex,settimeofday -F key=audit_time_rules |
Arbitrary changes to the system time can be used to obfuscate nefarious activities in log files, as well as to confuse network services that are highly dependent upon an accurate system time (such as sshd). All changes to the system time should be audited. |
4.1.3 | Record Attempts to Alter Time Through clock_settime |
If the auditd daemon is configured to use the
augenrules program to read audit rules during daemon startup (the
default), add the following line to a file with suffix .rules in the
directory /etc/audit/rules.d:
-a always,exit -F arch=b32 -S clock_settime -F a0=0x0 -F key=time-changeIf the system is 64 bit then also add the following line: -a always,exit -F arch=b64 -S clock_settime -F a0=0x0 -F key=time-changeIf the auditd daemon is configured to use the auditctl utility to read audit rules during daemon startup, add the following line to /etc/audit/audit.rules file: -a always,exit -F arch=b32 -S clock_settime -F a0=0x0 -F key=time-changeIf the system is 64 bit then also add the following line: -a always,exit -F arch=b64 -S clock_settime -F a0=0x0 -F key=time-changeThe -k option allows for the specification of a key in string form that can be used for better reporting capability through ausearch and aureport. Multiple system calls can be defined on the same line to save space if desired, but is not required. See an example of multiple combined syscalls: -a always,exit -F arch=b64 -S adjtimex,settimeofday -F key=audit_time_rules |
Arbitrary changes to the system time can be used to obfuscate nefarious activities in log files, as well as to confuse network services that are highly dependent upon an accurate system time (such as sshd). All changes to the system time should be audited. |
4.1.3 | Record attempts to alter time through adjtimex |
If the auditd daemon is configured to use the
augenrules program to read audit rules during daemon startup (the
default), add the following line to a file with suffix .rules in the
directory /etc/audit/rules.d:
-a always,exit -F arch=b32 -S adjtimex -F key=audit_time_rulesIf the system is 64 bit then also add the following line: -a always,exit -F arch=b64 -S adjtimex -F key=audit_time_rulesIf the auditd daemon is configured to use the auditctl utility to read audit rules during daemon startup, add the following line to /etc/audit/audit.rules file: -a always,exit -F arch=b32 -S adjtimex -F key=audit_time_rulesIf the system is 64 bit then also add the following line: -a always,exit -F arch=b64 -S adjtimex -F key=audit_time_rulesThe -k option allows for the specification of a key in string form that can be used for better reporting capability through ausearch and aureport. Multiple system calls can be defined on the same line to save space if desired, but is not required. See an example of multiple combined syscalls: -a always,exit -F arch=b64 -S adjtimex,settimeofday -F key=audit_time_rules |
Arbitrary changes to the system time can be used to obfuscate nefarious activities in log files, as well as to confuse network services that are highly dependent upon an accurate system time (such as sshd). All changes to the system time should be audited. |
4.1.3 | Record Attempts to Alter the localtime File |
If the auditd daemon is configured to use the
augenrules program to read audit rules during daemon startup (the default),
add the following line to a file with suffix .rules in the directory
/etc/audit/rules.d:
-w /etc/localtime -p wa -k audit_time_rulesIf the auditd daemon is configured to use the auditctl utility to read audit rules during daemon startup, add the following line to /etc/audit/audit.rules file: -w /etc/localtime -p wa -k audit_time_rulesThe -k option allows for the specification of a key in string form that can be used for better reporting capability through ausearch and aureport and should always be used. |
Arbitrary changes to the system time can be used to obfuscate nefarious activities in log files, as well as to confuse network services that are highly dependent upon an accurate system time (such as sshd). All changes to the system time should be audited. |
4.1.4 | Record Events that Modify User/Group Information - /etc/gshadow |
If the auditd daemon is configured to use the
augenrules program to read audit rules during daemon startup (the
default), add the following lines to a file with suffix .rules in the
directory /etc/audit/rules.d, in order to capture events that modify
account changes:
-w /etc/gshadow -p wa -k audit_rules_usergroup_modification If the auditd daemon is configured to use the auditctl utility to read audit rules during daemon startup, add the following lines to /etc/audit/audit.rules file, in order to capture events that modify account changes: -w /etc/gshadow -p wa -k audit_rules_usergroup_modification |
In addition to auditing new user and group accounts, these watches will alert the system administrator(s) to any modifications. Any unexpected users, groups, or modifications should be investigated for legitimacy. |
4.1.4 | Record Events that Modify User/Group Information - /etc/group |
If the auditd daemon is configured to use the
augenrules program to read audit rules during daemon startup (the
default), add the following lines to a file with suffix .rules in the
directory /etc/audit/rules.d, in order to capture events that modify
account changes:
-w /etc/group -p wa -k audit_rules_usergroup_modification If the auditd daemon is configured to use the auditctl utility to read audit rules during daemon startup, add the following lines to /etc/audit/audit.rules file, in order to capture events that modify account changes: -w /etc/group -p wa -k audit_rules_usergroup_modification |
In addition to auditing new user and group accounts, these watches will alert the system administrator(s) to any modifications. Any unexpected users, groups, or modifications should be investigated for legitimacy. |
4.1.4 | Record Events that Modify User/Group Information - /etc/security/opasswd |
If the auditd daemon is configured to use the
augenrules program to read audit rules during daemon startup (the
default), add the following lines to a file with suffix .rules in the
directory /etc/audit/rules.d, in order to capture events that modify
account changes:
-w /etc/security/opasswd -p wa -k audit_rules_usergroup_modification If the auditd daemon is configured to use the auditctl utility to read audit rules during daemon startup, add the following lines to /etc/audit/audit.rules file, in order to capture events that modify account changes: -w /etc/security/opasswd -p wa -k audit_rules_usergroup_modification |
In addition to auditing new user and group accounts, these watches will alert the system administrator(s) to any modifications. Any unexpected users, groups, or modifications should be investigated for legitimacy. |
4.1.4 | Record Events that Modify User/Group Information - /etc/shadow |
If the auditd daemon is configured to use the
augenrules program to read audit rules during daemon startup (the
default), add the following lines to a file with suffix .rules in the
directory /etc/audit/rules.d, in order to capture events that modify
account changes:
-w /etc/shadow -p wa -k audit_rules_usergroup_modification If the auditd daemon is configured to use the auditctl utility to read audit rules during daemon startup, add the following lines to /etc/audit/audit.rules file, in order to capture events that modify account changes: -w /etc/shadow -p wa -k audit_rules_usergroup_modification |
In addition to auditing new user and group accounts, these watches will alert the system administrator(s) to any modifications. Any unexpected users, groups, or modifications should be investigated for legitimacy. |
4.1.4 | Record Events that Modify User/Group Information - /etc/passwd |
If the auditd daemon is configured to use the
augenrules program to read audit rules during daemon startup (the
default), add the following lines to a file with suffix .rules in the
directory /etc/audit/rules.d, in order to capture events that modify
account changes:
-w /etc/passwd -p wa -k audit_rules_usergroup_modification If the auditd daemon is configured to use the auditctl utility to read audit rules during daemon startup, add the following lines to /etc/audit/audit.rules file, in order to capture events that modify account changes: -w /etc/passwd -p wa -k audit_rules_usergroup_modification |
In addition to auditing new user and group accounts, these watches will alert the system administrator(s) to any modifications. Any unexpected users, groups, or modifications should be investigated for legitimacy. |
4.1.5 | Record Events that Modify the System's Network Environment |
If the auditd daemon is configured to use the
augenrules program to read audit rules during daemon startup (the
default), add the following lines to a file with suffix .rules in the
directory /etc/audit/rules.d, setting ARCH to either b32 or b64 as
appropriate for your system:
-a always,exit -F arch=ARCH -S sethostname,setdomainname -F key=audit_rules_networkconfig_modification -w /etc/issue -p wa -k audit_rules_networkconfig_modification -w /etc/issue.net -p wa -k audit_rules_networkconfig_modification -w /etc/hosts -p wa -k audit_rules_networkconfig_modification -w /etc/sysconfig/network -p wa -k audit_rules_networkconfig_modificationIf the auditd daemon is configured to use the auditctl utility to read audit rules during daemon startup, add the following lines to /etc/audit/audit.rules file, setting ARCH to either b32 or b64 as appropriate for your system: -a always,exit -F arch=ARCH -S sethostname,setdomainname -F key=audit_rules_networkconfig_modification -w /etc/issue -p wa -k audit_rules_networkconfig_modification -w /etc/issue.net -p wa -k audit_rules_networkconfig_modification -w /etc/hosts -p wa -k audit_rules_networkconfig_modification -w /etc/sysconfig/network -p wa -k audit_rules_networkconfig_modification |
The network environment should not be modified by anything other than administrator action. Any change to network parameters should be audited. |
4.1.6 | Record Events that Modify the System's Mandatory Access Controls |
If the auditd daemon is configured to use the
augenrules program to read audit rules during daemon startup (the
default), add the following line to a file with suffix .rules in the
directory /etc/audit/rules.d:
-w /etc/selinux/ -p wa -k MAC-policyIf the auditd daemon is configured to use the auditctl utility to read audit rules during daemon startup, add the following line to /etc/audit/audit.rules file: -w /etc/selinux/ -p wa -k MAC-policy |
The system's mandatory access policy (SELinux) should not be arbitrarily changed by anything other than administrator action. All changes to MAC policy should be audited. |
4.1.7 | Record Attempts to Alter Logon and Logout Events - lastlog |
The audit system already collects login information for all users
and root. If the auditd daemon is configured to use the
augenrules program to read audit rules during daemon startup (the
default), add the following lines to a file with suffix .rules in the
directory /etc/audit/rules.d in order to watch for attempted manual
edits of files involved in storing logon events:
-w /var/log/lastlog -p wa -k loginsIf the auditd daemon is configured to use the auditctl utility to read audit rules during daemon startup, add the following lines to /etc/audit/audit.rules file in order to watch for unattempted manual edits of files involved in storing logon events: -w /var/log/lastlog -p wa -k logins |
Manual editing of these files may indicate nefarious activity, such as an attacker attempting to remove evidence of an intrusion. |
4.1.7 | Record Attempts to Alter Logon and Logout Events - faillock |
The audit system already collects login information for all users
and root. If the auditd daemon is configured to use the
augenrules program to read audit rules during daemon startup (the
default), add the following lines to a file with suffix .rules in the
directory /etc/audit/rules.d in order to watch for attempted manual
edits of files involved in storing logon events:
-w /var/run/faillock -p wa -k loginsIf the auditd daemon is configured to use the auditctl utility to read audit rules during daemon startup, add the following lines to /etc/audit/audit.rules file in order to watch for unattempted manual edits of files involved in storing logon events: -w /var/run/faillock -p wa -k logins |
Manual editing of these files may indicate nefarious activity, such as an attacker attempting to remove evidence of an intrusion. |
4.1.8 | Record Attempts to Alter Process and Session Initiation Information |
The audit system already collects process information for all
users and root. If the auditd daemon is configured to use the
augenrules program to read audit rules during daemon startup (the
default), add the following lines to a file with suffix .rules in the
directory /etc/audit/rules.d in order to watch for attempted manual
edits of files involved in storing such process information:
-w /var/run/utmp -p wa -k session -w /var/log/btmp -p wa -k session -w /var/log/wtmp -p wa -k sessionIf the auditd daemon is configured to use the auditctl utility to read audit rules during daemon startup, add the following lines to /etc/audit/audit.rules file in order to watch for attempted manual edits of files involved in storing such process information: -w /var/run/utmp -p wa -k session -w /var/log/btmp -p wa -k session -w /var/log/wtmp -p wa -k session |
Manual editing of these files may indicate nefarious activity, such as an attacker attempting to remove evidence of an intrusion. |
4.1.9 | Record Events that Modify the System's Discretionary Access Controls - fsetxattr |
At a minimum, the audit system should collect file permission
changes for all users and root. If the auditd daemon is configured
to use the augenrules program to read audit rules during daemon
startup (the default), add the following line to a file with suffix
.rules in the directory /etc/audit/rules.d:
-a always,exit -F arch=b32 -S fsetxattr -F auid>=1000 -F auid!=unset -F key=perm_modIf the system is 64 bit then also add the following line: -a always,exit -F arch=b64 -S fsetxattr -F auid>=1000 -F auid!=unset -F key=perm_modIf the auditd daemon is configured to use the auditctl utility to read audit rules during daemon startup, add the following line to /etc/audit/audit.rules file: -a always,exit -F arch=b32 -S fsetxattr -F auid>=1000 -F auid!=unset -F key=perm_modIf the system is 64 bit then also add the following line: -a always,exit -F arch=b64 -S fsetxattr -F auid>=1000 -F auid!=unset -F key=perm_mod |
The changing of file permissions could indicate that a user is attempting to gain access to information that would otherwise be disallowed. Auditing DAC modifications can facilitate the identification of patterns of abuse among both authorized and unauthorized users. |
4.1.9 | Record Events that Modify the System's Discretionary Access Controls - chmod |
At a minimum, the audit system should collect file permission
changes for all users and root. If the auditd daemon is configured to
use the augenrules program to read audit rules during daemon startup
(the default), add the following line to a file with suffix .rules in
the directory /etc/audit/rules.d:
-a always,exit -F arch=b32 -S chmod -F auid>=1000 -F auid!=unset -F key=perm_modIf the system is 64 bit then also add the following line: -a always,exit -F arch=b64 -S chmod -F auid>=1000 -F auid!=unset -F key=perm_modIf the auditd daemon is configured to use the auditctl utility to read audit rules during daemon startup, add the following line to /etc/audit/audit.rules file: -a always,exit -F arch=b32 -S chmod -F auid>=1000 -F auid!=unset -F key=perm_modIf the system is 64 bit then also add the following line: -a always,exit -F arch=b64 -S chmod -F auid>=1000 -F auid!=unset -F key=perm_mod |
The changing of file permissions could indicate that a user is attempting to gain access to information that would otherwise be disallowed. Auditing DAC modifications can facilitate the identification of patterns of abuse among both authorized and unauthorized users. |
4.1.9 | Record Events that Modify the System's Discretionary Access Controls - chown |
At a minimum, the audit system should collect file permission
changes for all users and root. If the auditd daemon is configured to
use the augenrules program to read audit rules during daemon startup
(the default), add the following line to a file with suffix .rules in
the directory /etc/audit/rules.d:
-a always,exit -F arch=b32 -S chown -F auid>=1000 -F auid!=unset -F key=perm_modIf the system is 64 bit then also add the following line: -a always,exit -F arch=b64 -S chown -F auid>=1000 -F auid!=unset -F key=perm_modIf the auditd daemon is configured to use the auditctl utility to read audit rules during daemon startup, add the following line to /etc/audit/audit.rules file: -a always,exit -F arch=b32 -S chown -F auid>=1000 -F auid!=unset -F key=perm_modIf the system is 64 bit then also add the following line: -a always,exit -F arch=b64 -S chown -F auid>=1000 -F auid!=unset -F key=perm_mod |
The changing of file permissions could indicate that a user is attempting to gain access to information that would otherwise be disallowed. Auditing DAC modifications can facilitate the identification of patterns of abuse among both authorized and unauthorized users. |
4.1.9 | Record Events that Modify the System's Discretionary Access Controls - fchownat |
At a minimum, the audit system should collect file permission
changes for all users and root. If the auditd daemon is configured
to use the augenrules program to read audit rules during daemon
startup (the default), add the following line to a file with suffix
.rules in the directory /etc/audit/rules.d:
-a always,exit -F arch=b32 -S fchownat -F auid>=1000 -F auid!=unset -F key=perm_modIf the system is 64 bit then also add the following line: -a always,exit -F arch=b64 -S fchownat -F auid>=1000 -F auid!=unset -F key=perm_modIf the auditd daemon is configured to use the auditctl utility to read audit rules during daemon startup, add the following line to /etc/audit/audit.rules file: -a always,exit -F arch=b32 -S fchownat -F auid>=1000 -F auid!=unset -F key=perm_modIf the system is 64 bit then also add the following line: -a always,exit -F arch=b64 -S fchownat -F auid>=1000 -F auid!=unset -F key=perm_mod |
The changing of file permissions could indicate that a user is attempting to gain access to information that would otherwise be disallowed. Auditing DAC modifications can facilitate the identification of patterns of abuse among both authorized and unauthorized users. |
4.1.9 | Record Events that Modify the System's Discretionary Access Controls - fchmod |
At a minimum, the audit system should collect file permission
changes for all users and root. If the auditd daemon is configured to
use the augenrules program to read audit rules during daemon startup
(the default), add the following line to a file with suffix .rules in
the directory /etc/audit/rules.d:
-a always,exit -F arch=b32 -S fchmod -F auid>=1000 -F auid!=unset -F key=perm_modIf the system is 64 bit then also add the following line: -a always,exit -F arch=b64 -S fchmod -F auid>=1000 -F auid!=unset -F key=perm_modIf the auditd daemon is configured to use the auditctl utility to read audit rules during daemon startup, add the following line to /etc/audit/audit.rules file: -a always,exit -F arch=b32 -S fchmod -F auid>=1000 -F auid!=unset -F key=perm_modIf the system is 64 bit then also add the following line: -a always,exit -F arch=b64 -S fchmod -F auid>=1000 -F auid!=unset -F key=perm_mod |
The changing of file permissions could indicate that a user is attempting to gain access to information that would otherwise be disallowed. Auditing DAC modifications can facilitate the identification of patterns of abuse among both authorized and unauthorized users. |
4.1.9 | Record Events that Modify the System's Discretionary Access Controls - removexattr |
At a minimum, the audit system should collect file permission
changes for all users and root.
If the auditd daemon is configured to use the augenrules program to read audit rules during daemon startup (the default), add the following line to a file with suffix .rules in the directory /etc/audit/rules.d: -a always,exit -F arch=b32 -S removexattr -F auid>=1000 -F auid!=unset -F key=perm_mod If the system is 64 bit then also add the following line: -a always,exit -F arch=b64 -S removexattr -F auid>=1000 -F auid!=unset -F key=perm_mod If the auditd daemon is configured to use the auditctl utility to read audit rules during daemon startup, add the following line to /etc/audit/audit.rules file: -a always,exit -F arch=b32 -S removexattr -F auid>=1000 -F auid!=unset -F key=perm_mod If the system is 64 bit then also add the following line: -a always,exit -F arch=b64 -S removexattr -F auid>=1000 -F auid!=unset -F key=perm_mod |
The changing of file permissions could indicate that a user is attempting to gain access to information that would otherwise be disallowed. Auditing DAC modifications can facilitate the identification of patterns of abuse among both authorized and unauthorized users. |
4.1.9 | Record Events that Modify the System's Discretionary Access Controls - fremovexattr |
At a minimum, the audit system should collect file permission
changes for all users and root.
If the auditd daemon is configured to use the augenrules program to read audit rules during daemon startup (the default), add the following line to a file with suffix .rules in the directory /etc/audit/rules.d: -a always,exit -F arch=b32 -S fremovexattr -F auid>=1000 -F auid!=unset -F key=perm_mod If the system is 64 bit then also add the following line: -a always,exit -F arch=b64 -S fremovexattr -F auid>=1000 -F auid!=unset -F key=perm_mod If the auditd daemon is configured to use the auditctl utility to read audit rules during daemon startup, add the following line to /etc/audit/audit.rules file: -a always,exit -F arch=b32 -S fremovexattr -F auid>=1000 -F auid!=unset -F key=perm_mod If the system is 64 bit then also add the following line: -a always,exit -F arch=b64 -S fremovexattr -F auid>=1000 -F auid!=unset -F key=perm_mod |
The changing of file permissions could indicate that a user is attempting to gain access to information that would otherwise be disallowed. Auditing DAC modifications can facilitate the identification of patterns of abuse among both authorized and unauthorized users. |
4.1.9 | Record Events that Modify the System's Discretionary Access Controls - lchown |
At a minimum, the audit system should collect file permission
changes for all users and root. If the auditd daemon is configured
to use the augenrules program to read audit rules during daemon
startup (the default), add the following line to a file with suffix
.rules in the directory /etc/audit/rules.d:
-a always,exit -F arch=b32 -S lchown -F auid>=1000 -F auid!=unset -F key=perm_modIf the system is 64 bit then also add the following line: -a always,exit -F arch=b64 -S lchown -F auid>=1000 -F auid!=unset -F key=perm_modIf the auditd daemon is configured to use the auditctl utility to read audit rules during daemon startup, add the following line to /etc/audit/audit.rules file: -a always,exit -F arch=b32 -S lchown -F auid>=1000 -F auid!=unset -F key=perm_modIf the system is 64 bit then also add the following line: -a always,exit -F arch=b64 -S lchown -F auid>=1000 -F auid!=unset -F key=perm_mod |
The changing of file permissions could indicate that a user is attempting to gain access to information that would otherwise be disallowed. Auditing DAC modifications can facilitate the identification of patterns of abuse among both authorized and unauthorized users. |
4.1.9 | Record Events that Modify the System's Discretionary Access Controls - lremovexattr |
At a minimum, the audit system should collect file permission
changes for all users and root.
If the auditd daemon is configured to use the augenrules program to read audit rules during daemon startup (the default), add the following line to a file with suffix .rules in the directory /etc/audit/rules.d: -a always,exit -F arch=b32 -S lremovexattr -F auid>=1000 -F auid!=unset -F key=perm_mod If the system is 64 bit then also add the following line: -a always,exit -F arch=b64 -S lremovexattr -F auid>=1000 -F auid!=unset -F key=perm_mod If the auditd daemon is configured to use the auditctl utility to read audit rules during daemon startup, add the following line to /etc/audit/audit.rules file: -a always,exit -F arch=b32 -S lremovexattr -F auid>=1000 -F auid!=unset -F key=perm_mod If the system is 64 bit then also add the following line: -a always,exit -F arch=b64 -S lremovexattr -F auid>=1000 -F auid!=unset -F key=perm_mod |
The changing of file permissions could indicate that a user is attempting to gain access to information that would otherwise be disallowed. Auditing DAC modifications can facilitate the identification of patterns of abuse among both authorized and unauthorized users. |
4.1.9 | Record Events that Modify the System's Discretionary Access Controls - setxattr |
At a minimum, the audit system should collect file permission
changes for all users and root. If the auditd daemon is configured
to use the augenrules program to read audit rules during daemon
startup (the default), add the following line to a file with suffix
.rules in the directory /etc/audit/rules.d:
-a always,exit -F arch=b32 -S setxattr -F auid>=1000 -F auid!=unset -F key=perm_modIf the system is 64 bit then also add the following line: -a always,exit -F arch=b64 -S setxattr -F auid>=1000 -F auid!=unset -F key=perm_modIf the auditd daemon is configured to use the auditctl utility to read audit rules during daemon startup, add the following line to /etc/audit/audit.rules file: -a always,exit -F arch=b32 -S setxattr -F auid>=1000 -F auid!=unset -F key=perm_modIf the system is 64 bit then also add the following line: -a always,exit -F arch=b64 -S setxattr -F auid>=1000 -F auid!=unset -F key=perm_mod |
The changing of file permissions could indicate that a user is attempting to gain access to information that would otherwise be disallowed. Auditing DAC modifications can facilitate the identification of patterns of abuse among both authorized and unauthorized users. |
4.1.9 | Record Events that Modify the System's Discretionary Access Controls - fchown |
At a minimum, the audit system should collect file permission
changes for all users and root. If the auditd daemon is configured
to use the augenrules program to read audit rules during daemon
startup (the default), add the following line to a file with suffix
.rules in the directory /etc/audit/rules.d:
-a always,exit -F arch=b32 -S fchown -F auid>=1000 -F auid!=unset -F key=perm_modIf the system is 64 bit then also add the following line: -a always,exit -F arch=b64 -S fchown -F auid>=1000 -F auid!=unset -F key=perm_modIf the auditd daemon is configured to use the auditctl utility to read audit rules during daemon startup, add the following line to /etc/audit/audit.rules file: -a always,exit -F arch=b32 -S fchown -F auid>=1000 -F auid!=unset -F key=perm_modIf the system is 64 bit then also add the following line: -a always,exit -F arch=b64 -S fchown -F auid>=1000 -F auid!=unset -F key=perm_mod |
The changing of file permissions could indicate that a user is attempting to gain access to information that would otherwise be disallowed. Auditing DAC modifications can facilitate the identification of patterns of abuse among both authorized and unauthorized users. |
4.1.9 | Record Events that Modify the System's Discretionary Access Controls - fchmodat |
At a minimum, the audit system should collect file permission
changes for all users and root. If the auditd daemon is configured to
use the augenrules program to read audit rules during daemon startup
(the default), add the following line to a file with suffix .rules in
the directory /etc/audit/rules.d:
-a always,exit -F arch=b32 -S fchmodat -F auid>=1000 -F auid!=unset -F key=perm_modIf the system is 64 bit then also add the following line: -a always,exit -F arch=b64 -S fchmodat -F auid>=1000 -F auid!=unset -F key=perm_modIf the auditd daemon is configured to use the auditctl utility to read audit rules during daemon startup, add the following line to /etc/audit/audit.rules file: -a always,exit -F arch=b32 -S fchmodat -F auid>=1000 -F auid!=unset -F key=perm_modIf the system is 64 bit then also add the following line: -a always,exit -F arch=b64 -S fchmodat -F auid>=1000 -F auid!=unset -F key=perm_mod |
The changing of file permissions could indicate that a user is attempting to gain access to information that would otherwise be disallowed. Auditing DAC modifications can facilitate the identification of patterns of abuse among both authorized and unauthorized users. |
4.1.9 | Record Events that Modify the System's Discretionary Access Controls - lsetxattr |
At a minimum, the audit system should collect file permission
changes for all users and root. If the auditd daemon is configured
to use the augenrules program to read audit rules during daemon
startup (the default), add the following line to a file with suffix
.rules in the directory /etc/audit/rules.d:
-a always,exit -F arch=b32 -S lsetxattr -F auid>=1000 -F auid!=unset -F key=perm_modIf the system is 64 bit then also add the following line: -a always,exit -F arch=b64 -S lsetxattr -F auid>=1000 -F auid!=unset -F key=perm_modIf the auditd daemon is configured to use the auditctl utility to read audit rules during daemon startup, add the following line to /etc/audit/audit.rules file: -a always,exit -F arch=b32 -S lsetxattr -F auid>=1000 -F auid!=unset -F key=perm_modIf the system is 64 bit then also add the following line: -a always,exit -F arch=b64 -S lsetxattr -F auid>=1000 -F auid!=unset -F key=perm_mod |
The changing of file permissions could indicate that a user is attempting to gain access to information that would otherwise be disallowed. Auditing DAC modifications can facilitate the identification of patterns of abuse among both authorized and unauthorized users. |
4.1.10 | Record Unsuccessful Access Attempts to Files - creat |
At a minimum, the audit system should collect unauthorized file
accesses for all users and root. If the auditd daemon is configured
to use the augenrules program to read audit rules during daemon
startup (the default), add the following lines to a file with suffix
.rules in the directory /etc/audit/rules.d:
-a always,exit -F arch=b32 -S creat -F exit=-EACCES -F auid>=1000 -F auid!=unset -F key=access -a always,exit -F arch=b32 -S creat -F exit=-EPERM -F auid>=1000 -F auid!=unset -F key=accessIf the system is 64 bit then also add the following lines: -a always,exit -F arch=b64 -S creat -F exit=-EACCES -F auid>=1000 -F auid!=unset -F key=access -a always,exit -F arch=b64 -S creat -F exit=-EPERM -F auid>=1000 -F auid!=unset -F key=accessIf the auditd daemon is configured to use the auditctl utility to read audit rules during daemon startup, add the following lines to /etc/audit/audit.rules file: -a always,exit -F arch=b32 -S creat -F exit=-EACCES -F auid>=1000 -F auid!=unset -F key=access -a always,exit -F arch=b32 -S creat -F exit=-EPERM -F auid>=1000 -F auid!=unset -F key=accessIf the system is 64 bit then also add the following lines: -a always,exit -F arch=b64 -S creat -F exit=-EACCES -F auid>=1000 -F auid!=unset -F key=access -a always,exit -F arch=b64 -S creat -F exit=-EPERM -F auid>=1000 -F auid!=unset -F key=access |
Unsuccessful attempts to access files could be an indicator of malicious activity on a system. Auditing these events could serve as evidence of potential system compromise. |
4.1.10 | Record Unsuccessful Access Attempts to Files - ftruncate |
At a minimum, the audit system should collect unauthorized file
accesses for all users and root. If the auditd daemon is configured
to use the augenrules program to read audit rules during daemon
startup (the default), add the following lines to a file with suffix
.rules in the directory /etc/audit/rules.d:
-a always,exit -F arch=b32 -S ftruncate -F exit=-EACCES -F auid>=1000 -F auid!=unset -F key=access -a always,exit -F arch=b32 -S ftruncate -F exit=-EPERM -F auid>=1000 -F auid!=unset -F key=accessIf the system is 64 bit then also add the following lines: -a always,exit -F arch=b64 -S ftruncate -F exit=-EACCES -F auid>=1000 -F auid!=unset -F key=access -a always,exit -F arch=b64 -S ftruncate -F exit=-EPERM -F auid>=1000 -F auid!=unset -F key=accessIf the auditd daemon is configured to use the auditctl utility to read audit rules during daemon startup, add the following lines to /etc/audit/audit.rules file: -a always,exit -F arch=b32 -S ftruncate -F exit=-EACCES -F auid>=1000 -F auid!=unset -F key=access -a always,exit -F arch=b32 -S ftruncate -F exit=-EPERM -F auid>=1000 -F auid!=unset -F key=accessIf the system is 64 bit then also add the following lines: -a always,exit -F arch=b64 -S ftruncate -F exit=-EACCES -F auid>=1000 -F auid!=unset -F key=access -a always,exit -F arch=b64 -S ftruncate -F exit=-EPERM -F auid>=1000 -F auid!=unset -F key=access |
Unsuccessful attempts to access files could be an indicator of malicious activity on a system. Auditing these events could serve as evidence of potential system compromise. |
4.1.10 | Record Unsuccessful Access Attempts to Files - openat |
At a minimum, the audit system should collect unauthorized file
accesses for all users and root. If the auditd daemon is configured
to use the augenrules program to read audit rules during daemon
startup (the default), add the following lines to a file with suffix
.rules in the directory /etc/audit/rules.d:
-a always,exit -F arch=b32 -S openat -F exit=-EACCES -F auid>=1000 -F auid!=unset -F key=access -a always,exit -F arch=b32 -S openat -F exit=-EPERM -F auid>=1000 -F auid!=unset -F key=accessIf the system is 64 bit then also add the following lines: -a always,exit -F arch=b64 -S openat -F exit=-EACCES -F auid>=1000 -F auid!=unset -F key=access -a always,exit -F arch=b64 -S openat -F exit=-EPERM -F auid>=1000 -F auid!=unset -F key=accessIf the auditd daemon is configured to use the auditctl utility to read audit rules during daemon startup, add the following lines to /etc/audit/audit.rules file: -a always,exit -F arch=b32 -S openat -F exit=-EACCES -F auid>=1000 -F auid!=unset -F key=access -a always,exit -F arch=b32 -S openat -F exit=-EPERM -F auid>=1000 -F auid!=unset -F key=accessIf the system is 64 bit then also add the following lines: -a always,exit -F arch=b64 -S openat -F exit=-EACCES -F auid>=1000 -F auid!=unset -F key=access -a always,exit -F arch=b64 -S openat -F exit=-EPERM -F auid>=1000 -F auid!=unset -F key=access |
Unsuccessful attempts to access files could be an indicator of malicious activity on a system. Auditing these events could serve as evidence of potential system compromise. |
4.1.10 | Record Unsuccessful Access Attempts to Files - truncate |
At a minimum, the audit system should collect unauthorized file
accesses for all users and root. If the auditd daemon is configured
to use the augenrules program to read audit rules during daemon
startup (the default), add the following lines to a file with suffix
.rules in the directory /etc/audit/rules.d:
-a always,exit -F arch=b32 -S truncate -F exit=-EACCES -F auid>=1000 -F auid!=unset -F key=access -a always,exit -F arch=b32 -S truncate -F exit=-EPERM -F auid>=1000 -F auid!=unset -F key=accessIf the system is 64 bit then also add the following lines: -a always,exit -F arch=b64 -S truncate -F exit=-EACCES -F auid>=1000 -F auid!=unset -F key=access -a always,exit -F arch=b64 -S truncate -F exit=-EPERM -F auid>=1000 -F auid!=unset -F key=accessIf the auditd daemon is configured to use the auditctl utility to read audit rules during daemon startup, add the following lines to /etc/audit/audit.rules file: -a always,exit -F arch=b32 -S truncate -F exit=-EACCES -F auid>=1000 -F auid!=unset -F key=access -a always,exit -F arch=b32 -S truncate -F exit=-EPERM -F auid>=1000 -F auid!=unset -F key=accessIf the system is 64 bit then also add the following lines: -a always,exit -F arch=b64 -S truncate -F exit=-EACCES -F auid>=1000 -F auid!=unset -F key=access -a always,exit -F arch=b64 -S truncate -F exit=-EPERM -F auid>=1000 -F auid!=unset -F key=access |
Unsuccessful attempts to access files could be an indicator of malicious activity on a system. Auditing these events could serve as evidence of potential system compromise. |
4.1.10 | Record Unsuccessful Access Attempts to Files - open |
At a minimum, the audit system should collect unauthorized file
accesses for all users and root. If the auditd daemon is configured
to use the augenrules program to read audit rules during daemon
startup (the default), add the following lines to a file with suffix
.rules in the directory /etc/audit/rules.d:
-a always,exit -F arch=b32 -S open -F exit=-EACCES -F auid>=1000 -F auid!=unset -F key=access -a always,exit -F arch=b32 -S open -F exit=-EPERM -F auid>=1000 -F auid!=unset -F key=accessIf the system is 64 bit then also add the following lines: -a always,exit -F arch=b64 -S open -F exit=-EACCES -F auid>=1000 -F auid!=unset -F key=access -a always,exit -F arch=b64 -S open -F exit=-EPERM -F auid>=1000 -F auid!=unset -F key=accessIf the auditd daemon is configured to use the auditctl utility to read audit rules during daemon startup, add the following lines to /etc/audit/audit.rules file: -a always,exit -F arch=b32 -S open -F exit=-EACCES -F auid>=1000 -F auid!=unset -F key=access -a always,exit -F arch=b32 -S open -F exit=-EPERM -F auid>=1000 -F auid!=unset -F key=accessIf the system is 64 bit then also add the following lines: -a always,exit -F arch=b64 -S open -F exit=-EACCES -F auid>=1000 -F auid!=unset -F key=access -a always,exit -F arch=b64 -S open -F exit=-EPERM -F auid>=1000 -F auid!=unset -F key=access |
Unsuccessful attempts to access files could be an indicator of malicious activity on a system. Auditing these events could serve as evidence of potential system compromise. |
4.1.11 | Record Unsuccessful Access Attempts to Files - open_by_handle_at |
At a minimum, the audit system should collect unauthorized file
accesses for all users and root. If the auditd daemon is configured
to use the augenrules program to read audit rules during daemon
startup (the default), add the following lines to a file with suffix
.rules in the directory /etc/audit/rules.d:
-a always,exit -F arch=b32 -S open_by_handle_at -F exit=-EACCES -F auid>=1000 -F auid!=unset -F key=access -a always,exit -F arch=b32 -S open_by_handle_at -F exit=-EPERM -F auid>=1000 -F auid!=unset -F key=accessIf the system is 64 bit then also add the following lines: -a always,exit -F arch=b64 -S open_by_handle_at -F exit=-EACCES -F auid>=1000 -F auid!=unset -F key=access -a always,exit -F arch=b64 -S open_by_handle_at -F exit=-EPERM -F auid>=1000 -F auid!=unset -F key=accessIf the auditd daemon is configured to use the auditctl utility to read audit rules during daemon startup, add the following lines to /etc/audit/audit.rules file: -a always,exit -F arch=b32 -S open_by_handle_at,truncate,ftruncate -F exit=-EACCES -F auid>=1000 -F auid!=unset -F key=access -a always,exit -F arch=b32 -S open_by_handle_at,truncate,ftruncate -F exit=-EPERM -F auid>=1000 -F auid!=unset -F key=accessIf the system is 64 bit then also add the following lines: -a always,exit -F arch=b64 -S open_by_handle_at,truncate,ftruncate -F exit=-EACCES -F auid>=1000 -F auid!=unset -F key=access -a always,exit -F arch=b64 -S open_by_handle_at,truncate,ftruncate -F exit=-EPERM -F auid>=1000 -F auid!=unset -F key=access |
Unsuccessful attempts to access files could be an indicator of malicious activity on a system. Auditing these events could serve as evidence of potential system compromise. |
4.1.12 | Ensure auditd Collects Information on the Use of Privileged Commands |
The audit system should collect information about usage of privileged
commands for all users and root. To find the relevant setuid /
setgid programs, run the following command for each local partition
PART:
$ sudo find PART -xdev -type f -perm -4000 -o -type f -perm -2000 2>/dev/nullIf the auditd daemon is configured to use the augenrules program to read audit rules during daemon startup (the default), add a line of the following form to a file with suffix .rules in the directory /etc/audit/rules.d for each setuid / setgid program on the system, replacing the SETUID_PROG_PATH part with the full path of that setuid / setgid program in the list: -a always,exit -F path=SETUID_PROG_PATH -F auid>=1000 -F auid!=unset -F key=privilegedIf the auditd daemon is configured to use the auditctl utility to read audit rules during daemon startup, add a line of the following form to /etc/audit/audit.rules for each setuid / setgid program on the system, replacing the SETUID_PROG_PATH part with the full path of that setuid / setgid program in the list: -a always,exit -F path=SETUID_PROG_PATH -F auid>=1000 -F auid!=unset -F key=privileged |
Misuse of privileged functions, either intentionally or unintentionally by
authorized users, or by unauthorized external entities that have compromised system accounts,
is a serious and ongoing concern and can have significant adverse impacts on organizations.
Auditing the use of privileged functions is one way to detect such misuse and identify
the risk from insider and advanced persistent threats.
Privileged programs are subject to escalation-of-privilege attacks, which attempt to subvert their normal role of providing some necessary but limited capability. As such, motivation exists to monitor these programs for unusual activity. |
4.1.12 | Ensure auditd Collects Information on Exporting to Media (successful) |
At a minimum, the audit system should collect media exportation
events for all users and root. If the auditd daemon is configured to
use the augenrules program to read audit rules during daemon startup
(the default), add the following line to a file with suffix .rules in
the directory /etc/audit/rules.d, setting ARCH to either b32 or b64 as
appropriate for your system:
-a always,exit -F arch=ARCH -S mount -F auid>=1000 -F auid!=unset -F key=exportIf the auditd daemon is configured to use the auditctl utility to read audit rules during daemon startup, add the following line to /etc/audit/audit.rules file, setting ARCH to either b32 or b64 as appropriate for your system: -a always,exit -F arch=ARCH -S mount -F auid>=1000 -F auid!=unset -F key=export |
The unauthorized exportation of data to external media could result in an information leak where classified information, Privacy Act information, and intellectual property could be lost. An audit trail should be created each time a filesystem is mounted to help identify and guard against information loss. |
4.1.13 | Ensure auditd Collects File Deletion Events by User - unlinkat |
At a minimum, the audit system should collect file deletion events
for all users and root. If the auditd daemon is configured to use the
augenrules program to read audit rules during daemon startup (the
default), add the following line to a file with suffix .rules in the
directory /etc/audit/rules.d, setting ARCH to either b32 or b64 as
appropriate for your system:
-a always,exit -F arch=ARCH -S unlinkat -F auid>=1000 -F auid!=unset -F key=deleteIf the auditd daemon is configured to use the auditctl utility to read audit rules during daemon startup, add the following line to /etc/audit/audit.rules file, setting ARCH to either b32 or b64 as appropriate for your system: -a always,exit -F arch=ARCH -S unlinkat -F auid>=1000 -F auid!=unset -F key=delete |
Auditing file deletions will create an audit trail for files that are removed from the system. The audit trail could aid in system troubleshooting, as well as, detecting malicious processes that attempt to delete log files to conceal their presence. |
4.1.13 | Ensure auditd Collects File Deletion Events by User - unlink |
At a minimum, the audit system should collect file deletion events
for all users and root. If the auditd daemon is configured to use the
augenrules program to read audit rules during daemon startup (the
default), add the following line to a file with suffix .rules in the
directory /etc/audit/rules.d, setting ARCH to either b32 or b64 as
appropriate for your system:
-a always,exit -F arch=ARCH -S unlink -F auid>=1000 -F auid!=unset -F key=deleteIf the auditd daemon is configured to use the auditctl utility to read audit rules during daemon startup, add the following line to /etc/audit/audit.rules file, setting ARCH to either b32 or b64 as appropriate for your system: -a always,exit -F arch=ARCH -S unlink -F auid>=1000 -F auid!=unset -F key=delete |
Auditing file deletions will create an audit trail for files that are removed from the system. The audit trail could aid in system troubleshooting, as well as, detecting malicious processes that attempt to delete log files to conceal their presence. |
4.1.13 | Ensure auditd Collects File Deletion Events by User - renameat |
At a minimum, the audit system should collect file deletion events
for all users and root. If the auditd daemon is configured to use the
augenrules program to read audit rules during daemon startup (the
default), add the following line to a file with suffix .rules in the
directory /etc/audit/rules.d, setting ARCH to either b32 or b64 as
appropriate for your system:
-a always,exit -F arch=ARCH -S renameat -F auid>=1000 -F auid!=unset -F key=deleteIf the auditd daemon is configured to use the auditctl utility to read audit rules during daemon startup, add the following line to /etc/audit/audit.rules file, setting ARCH to either b32 or b64 as appropriate for your system: -a always,exit -F arch=ARCH -S renameat -F auid>=1000 -F auid!=unset -F key=delete |
Auditing file deletions will create an audit trail for files that are removed from the system. The audit trail could aid in system troubleshooting, as well as, detecting malicious processes that attempt to delete log files to conceal their presence. |
4.1.13 | Ensure auditd Collects File Deletion Events by User - rename |
At a minimum, the audit system should collect file deletion events
for all users and root. If the auditd daemon is configured to use the
augenrules program to read audit rules during daemon startup (the
default), add the following line to a file with suffix .rules in the
directory /etc/audit/rules.d, setting ARCH to either b32 or b64 as
appropriate for your system:
-a always,exit -F arch=ARCH -S rename -F auid>=1000 -F auid!=unset -F key=deleteIf the auditd daemon is configured to use the auditctl utility to read audit rules during daemon startup, add the following line to /etc/audit/audit.rules file, setting ARCH to either b32 or b64 as appropriate for your system: -a always,exit -F arch=ARCH -S rename -F auid>=1000 -F auid!=unset -F key=delete |
Auditing file deletions will create an audit trail for files that are removed from the system. The audit trail could aid in system troubleshooting, as well as, detecting malicious processes that attempt to delete log files to conceal their presence. |
4.1.14 | Ensure auditd Collects System Administrator Actions |
At a minimum, the audit system should collect administrator actions
for all users and root. If the auditd daemon is configured to use the
augenrules program to read audit rules during daemon startup (the default),
add the following line to a file with suffix .rules in the directory
/etc/audit/rules.d:
-w /etc/sudoers -p wa -k actions -w /etc/sudoers.d/ -p wa -k actionsIf the auditd daemon is configured to use the auditctl utility to read audit rules during daemon startup, add the following line to /etc/audit/audit.rules file: -w /etc/sudoers -p wa -k actions -w /etc/sudoers.d/ -p wa -k actions |
The actions taken by system administrators should be audited to keep a record of what was executed on the system, as well as, for accountability purposes. |
4.1.14 | Ensure auditd Collects File Deletion Events by User |
At a minimum the audit system should collect file deletion events
for all users and root. If the auditd daemon is configured to use the
augenrules program to read audit rules during daemon startup (the
default), add the following line to a file with suffix .rules in the
directory /etc/audit/rules.d, setting ARCH to either b32 or b64 as
appropriate for your system:
-a always,exit -F arch=ARCH -S rmdir,unlink,unlinkat,rename,renameat -F auid>=1000 -F auid!=unset -F key=deleteIf the auditd daemon is configured to use the auditctl utility to read audit rules during daemon startup, add the following line to /etc/audit/audit.rules file, setting ARCH to either b32 or b64 as appropriate for your system: -a always,exit -F arch=ARCH -S rmdir,unlink,unlinkat,rename -S renameat -F auid>=1000 -F auid!=unset -F key=delete |
Auditing file deletions will create an audit trail for files that are removed from the system. The audit trail could aid in system troubleshooting, as well as, detecting malicious processes that attempt to delete log files to conceal their presence. |
4.1.14 | Ensure auditd Collects File Deletion Events by User - rmdir |
At a minimum, the audit system should collect file deletion events
for all users and root. If the auditd daemon is configured to use the
augenrules program to read audit rules during daemon startup (the
default), add the following line to a file with suffix .rules in the
directory /etc/audit/rules.d, setting ARCH to either b32 or b64 as
appropriate for your system:
-a always,exit -F arch=ARCH -S rmdir -F auid>=1000 -F auid!=unset -F key=deleteIf the auditd daemon is configured to use the auditctl utility to read audit rules during daemon startup, add the following line to /etc/audit/audit.rules file, setting ARCH to either b32 or b64 as appropriate for your system: -a always,exit -F arch=ARCH -S rmdir -F auid>=1000 -F auid!=unset -F key=delete |
Auditing file deletions will create an audit trail for files that are removed from the system. The audit trail could aid in system troubleshooting, as well as, detecting malicious processes that attempt to delete log files to conceal their presence. |
4.1.16 | Ensure auditd Collects Information on the Use of Privileged Commands - insmod |
At a minimum, the audit system should collect the execution of
privileged commands for all users and root. If the auditd daemon is
configured to use the augenrules program to read audit rules during
daemon startup (the default), add a line of the following form to a file with
suffix .rules in the directory /etc/audit/rules.d:
-w /sbin/insmod -p x -k modules |
Misuse of privileged functions, either intentionally or unintentionally by
authorized users, or by unauthorized external entities that have compromised system accounts,
is a serious and ongoing concern and can have significant adverse impacts on organizations.
Auditing the use of privileged functions is one way to detect such misuse and identify
the risk from insider and advanced persistent threats.
Privileged programs are subject to escalation-of-privilege attacks, which attempt to subvert their normal role of providing some necessary but limited capability. As such, motivation exists to monitor these programs for unusual activity. |
4.1.16 | Ensure auditd Collects Information on the Use of Privileged Commands - rmmod |
At a minimum, the audit system should collect the execution of
privileged commands for all users and root. If the auditd daemon is
configured to use the augenrules program to read audit rules during
daemon startup (the default), add a line of the following form to a file with
suffix .rules in the directory /etc/audit/rules.d:
-w /sbin/rmmod -p x -k modules |
Misuse of privileged functions, either intentionally or unintentionally by
authorized users, or by unauthorized external entities that have compromised system accounts,
is a serious and ongoing concern and can have significant adverse impacts on organizations.
Auditing the use of privileged functions is one way to detect such misuse and identify
the risk from insider and advanced persistent threats.
Privileged programs are subject to escalation-of-privilege attacks, which attempt to subvert their normal role of providing some necessary but limited capability. As such, motivation exists to monitor these programs for unusual activity. |
4.1.16 | Ensure auditd Collects Information on Kernel Module Loading - init_module |
To capture kernel module loading events, use following line, setting ARCH to
either b32 for 32-bit system, or having two lines for both b32 and b64 in case your system is 64-bit:
-a always,exit -F arch=ARCH -S init_module -F auid>=1000 -F auid!=unset -F key=modulesPlace to add the line depends on a way auditd daemon is configured. If it is configured to use the augenrules program (the default), add the line to a file with suffix .rules in the directory /etc/audit/rules.d. If the auditd daemon is configured to use the auditctl utility, add the line to file /etc/audit/audit.rules. |
The addition of kernel modules can be used to alter the behavior of the kernel and potentially introduce malicious code into kernel space. It is important to have an audit trail of modules that have been introduced into the kernel. |
4.1.16 | Ensure auditd Collects Information on the Use of Privileged Commands - modprobe |
At a minimum, the audit system should collect the execution of
privileged commands for all users and root. If the auditd daemon is
configured to use the augenrules program to read audit rules during
daemon startup (the default), add a line of the following form to a file with
suffix .rules in the directory /etc/audit/rules.d:
-w /sbin/modprobe -p x -k modulesIf the auditd daemon is configured to use the auditctl utility to read audit rules during daemon startup, add a line of the following form to /etc/audit/audit.rules: -w /sbin/modprobe -p x -k modules |
Misuse of privileged functions, either intentionally or unintentionally by
authorized users, or by unauthorized external entities that have compromised system accounts,
is a serious and ongoing concern and can have significant adverse impacts on organizations.
Auditing the use of privileged functions is one way to detect such misuse and identify
the risk from insider and advanced persistent threats.
Privileged programs are subject to escalation-of-privilege attacks, which attempt to subvert their normal role of providing some necessary but limited capability. As such, motivation exists to monitor these programs for unusual activity. |
4.1.16 | Ensure auditd Collects Information on Kernel Module Unloading - delete_module |
To capture kernel module unloading events, use following line, setting ARCH to
either b32 for 32-bit system, or having two lines for both b32 and b64 in case your system is 64-bit:
-a always,exit -F arch=ARCH -S delete_module -F auid>=1000 -F auid!=unset -F key=modulesPlace to add the line depends on a way auditd daemon is configured. If it is configured to use the augenrules program (the default), add the line to a file with suffix .rules in the directory /etc/audit/rules.d. If the auditd daemon is configured to use the auditctl utility, add the line to file /etc/audit/audit.rules. |
The removal of kernel modules can be used to alter the behavior of the kernel and potentially introduce malicious code into kernel space. It is important to have an audit trail of modules that have been introduced into the kernel. |
4.1.17 | Ensure auditd Collects Information on Kernel Module Loading and Unloading - finit_module |
If the auditd daemon is configured to use the augenrules program
to read audit rules during daemon startup (the default), add the following lines to a file
with suffix .rules in the directory /etc/audit/rules.d to capture kernel module
loading and unloading events, setting ARCH to either b32 or b64 as appropriate for your system:
-a always,exit -F arch=ARCH -S finit_module -F auid>=1000 -F auid!=unset -F key=modulesIf the auditd daemon is configured to use the auditctl utility to read audit rules during daemon startup, add the following lines to /etc/audit/audit.rules file in order to capture kernel module loading and unloading events, setting ARCH to either b32 or b64 as appropriate for your system: -a always,exit -F arch=ARCH -S finit_module -F auid>=1000 -F auid!=unset -F key=modules |
The addition/removal of kernel modules can be used to alter the behavior of the kernel and potentially introduce malicious code into kernel space. It is important to have an audit trail of modules that have been introduced into the kernel. |
4.1.17 | Ensure auditd Collects Information on Kernel Module Loading and Unloading |
To capture kernel module loading and unloading events, use following lines, setting ARCH to
either b32 for 32-bit system, or having two lines for both b32 and b64 in case your system is 64-bit:
-a always,exit -F arch=ARCH -S init_module,finit_module,delete_module -F key=modulesThe place to add the lines depends on a way auditd daemon is configured. If it is configured to use the augenrules program (the default), add the lines to a file with suffix .rules in the directory /etc/audit/rules.d. If the auditd daemon is configured to use the auditctl utility, add the lines to file /etc/audit/audit.rules. |
The addition/removal of kernel modules can be used to alter the behavior of the kernel and potentially introduce malicious code into kernel space. It is important to have an audit trail of modules that have been introduced into the kernel. |
4.1.17 | Make the auditd Configuration Immutable |
If the auditd daemon is configured to use the
augenrules program to read audit rules during daemon startup (the
default), add the following line to a file with suffix .rules in the
directory /etc/audit/rules.d in order to make the auditd configuration
immutable:
-e 2If the auditd daemon is configured to use the auditctl utility to read audit rules during daemon startup, add the following line to /etc/audit/audit.rules file in order to make the auditd configuration immutable: -e 2With this setting, a reboot will be required to change any audit rules. |
Making the audit configuration immutable prevents accidental as well as malicious modification of the audit rules, although it may be problematic if legitimate changes are needed during system operation. |
4.2.1.1 | Ensure rsyslog is Installed |
Rsyslog is installed by default. The rsyslog package can be installed with the following command: $ sudo yum install rsyslog |
The rsyslog package provides the rsyslog daemon, which provides system logging services. |
4.2.1.2 | Enable rsyslog Service |
The rsyslog service provides syslog-style logging by default on Red Hat Enterprise Linux 7.
The rsyslog service can be enabled with the following command:
$ sudo systemctl enable rsyslog.service |
The rsyslog service must be running in order to provide logging services, which are essential to system administration. |
4.2.1.3 | Ensure System Log Files Have Correct Permissions |
The file permissions for all log files written by rsyslog should
be set to 600, or more restrictive. These log files are determined by the
second part of each Rule line in /etc/rsyslog.conf and typically
all appear in /var/log. For each log file LOGFILE
referenced in /etc/rsyslog.conf, run the following command to
inspect the file's permissions:
$ ls -l LOGFILEIf the permissions are not 600 or more restrictive, run the following command to correct this: $ sudo chmod 0600 LOGFILE" |
Log files can contain valuable information regarding system configuration. If the system log files are not protected unauthorized users could change the logged data, eliminating their forensic value. |
4.2.1.4 | Ensure Logs Sent To Remote Host |
To configure rsyslog to send logs to a remote log server,
open /etc/rsyslog.conf and read and understand the last section of the file,
which describes the multiple directives necessary to activate remote
logging.
Along with these other directives, the system can be configured
to forward its logs to a particular log server by
adding or correcting one of the following lines,
substituting logcollector appropriately.
The choice of protocol depends on the environment of the system;
although TCP and RELP provide more reliable message delivery,
they may not be supported in all environments.
To use UDP for log message delivery: *.* @logcollector To use TCP for log message delivery: *.* @@logcollector To use RELP for log message delivery: *.* :omrelp:logcollector There must be a resolvable DNS CNAME or Alias record set to "logcollector" for logs to be sent correctly to the centralized logging utility. |
A log server (loghost) receives syslog messages from one or more systems. This data can be used as an additional log source in the event a system is compromised and its local logs are suspect. Forwarding log messages to a remote loghost also provides system administrators with a centralized place to view the status of multiple hosts within the enterprise. |
4.2.1.5 | Enable rsyslog to Accept Messages via UDP, if Acting As Log Server |
The rsyslog daemon should not accept remote messages
unless the system acts as a log server.
If the system needs to act as a central log server, add the following lines to
/etc/rsyslog.conf to enable reception of messages over UDP:
$ModLoad imudp $UDPServerRun 514 |
Many devices, such as switches, routers, and other Unix-like systems, may only support the traditional syslog transmission over UDP. If the system must act as a log server, this enables it to receive their messages as well. |
4.2.1.5 | Enable rsyslog to Accept Messages via TCP, if Acting As Log Server |
The rsyslog daemon should not accept remote messages
unless the system acts as a log server.
If the system needs to act as a central log server, add the following lines to
/etc/rsyslog.conf to enable reception of messages over TCP:
$ModLoad imtcp $InputTCPServerRun 514 |
If the system needs to act as a log server, this ensures that it can receive messages over a reliable TCP connection. |
4.2.1.5 | Ensure rsyslog Does Not Accept Remote Messages Unless Acting As Log Server |
The rsyslog daemon should not accept remote messages
unless the system acts as a log server.
To ensure that it is not listening on the network, ensure the following lines are
not found in /etc/rsyslog.conf:
$ModLoad imtcp $InputTCPServerRun port $ModLoad imudp $UDPServerRun port $ModLoad imrelp $InputRELPServerRun port |
Any process which receives messages from the network incurs some risk of receiving malicious messages. This risk can be eliminated for rsyslog by configuring it not to listen on the network. |
4.2.2.1 | Ensure journald is configured to send logs to rsyslog | Data from journald may be stored in volatile memory or persisted locally. Utilities exist to accept remote export of journald logs. | Storing log data on a remote host protects log integrity from local attacks. If an attacker gains root access on the local system, they could tamper with or remove log data that is stored on the local system. |
4.2.2.2 | Ensure journald is configured to compress large log files | The journald system can compress large log files to avoid fill the system disk. | Log files that are not properly compressed run the risk of growing so large that they fill up the log partition. Valuable logging information could be lost if the log partition becomes full. |
4.2.2.3 | Ensure journald is configured to write log files to persistent disk | The journald system may store log files in volatile memory or locally on disk. If the logs are only stored in volatile memory they will we lost upon reboot. | Log files contain valuable data and need to be persistent to aid in possible investigations. |
4.3 | Ensure Logrotate Runs Periodically |
The logrotate utility allows for the automatic rotation of
log files. The frequency of rotation is specified in /etc/logrotate.conf,
which triggers a cron task. To configure logrotate to run daily, add or correct
the following line in /etc/logrotate.conf:
# rotate log files frequency daily |
Log files that are not properly rotated run the risk of growing so large that they fill up the /var/log partition. Valuable logging information could be lost if the /var/log partition becomes full. |
5.1.1 | Enable cron Service |
The crond service is used to execute commands at
preconfigured times. It is required by almost all systems to perform necessary
maintenance tasks, such as notifying root of system activity.
The crond service can be enabled with the following command:
$ sudo systemctl enable crond.service |
Due to its usage for maintenance and security-supporting tasks, enabling the cron daemon is essential. |
5.1.2 | Verify Group Who Owns Crontab |
To properly set the group owner of /etc/crontab , run the command:
$ sudo chgrp root /etc/crontab |
Service configuration files enable or disable features of their respective services that if configured incorrectly can lead to insecure and vulnerable configurations. Therefore, service configuration files should be owned by the correct group to prevent unauthorized changes. |
5.1.2 | Verify Permissions on crontab |
To properly set the permissions of /etc/crontab , run the command:
$ sudo chmod 0600 /etc/crontab |
Service configuration files enable or disable features of their respective services that if configured incorrectly can lead to insecure and vulnerable configurations. Therefore, service configuration files should have the correct access rights to prevent unauthorized changes. |
5.1.2 | Verify Owner on crontab |
To properly set the owner of /etc/crontab , run the command:
$ sudo chown root /etc/crontab |
Service configuration files enable or disable features of their respective services that if configured incorrectly can lead to insecure and vulnerable configurations. Therefore, service configuration files should be owned by the correct user to prevent unauthorized changes. |
5.1.3 | Verify Group Who Owns cron.hourly |
To properly set the group owner of /etc/cron.hourly , run the command:
$ sudo chgrp root /etc/cron.hourly |
Service configuration files enable or disable features of their respective services that if configured incorrectly can lead to insecure and vulnerable configurations. Therefore, service configuration files should be owned by the correct group to prevent unauthorized changes. |
5.1.3 | Verify Owner on cron.hourly |
To properly set the owner of /etc/cron.hourly , run the command:
$ sudo chown root /etc/cron.hourly |
Service configuration files enable or disable features of their respective services that if configured incorrectly can lead to insecure and vulnerable configurations. Therefore, service configuration files should be owned by the correct user to prevent unauthorized changes. |
5.1.3 | Verify Permissions on cron.hourly |
To properly set the permissions of /etc/cron.hourly , run the command:
$ sudo chmod 0700 /etc/cron.hourly |
Service configuration files enable or disable features of their respective services that if configured incorrectly can lead to insecure and vulnerable configurations. Therefore, service configuration files should have the correct access rights to prevent unauthorized changes. |
5.1.4 | Verify Owner on cron.daily |
To properly set the owner of /etc/cron.daily , run the command:
$ sudo chown root /etc/cron.daily |
Service configuration files enable or disable features of their respective services that if configured incorrectly can lead to insecure and vulnerable configurations. Therefore, service configuration files should be owned by the correct user to prevent unauthorized changes. |
5.1.4 | Verify Group Who Owns cron.daily |
To properly set the group owner of /etc/cron.daily , run the command:
$ sudo chgrp root /etc/cron.daily |
Service configuration files enable or disable features of their respective services that if configured incorrectly can lead to insecure and vulnerable configurations. Therefore, service configuration files should be owned by the correct group to prevent unauthorized changes. |
5.1.4 | Verify Permissions on cron.daily |
To properly set the permissions of /etc/cron.daily , run the command:
$ sudo chmod 0700 /etc/cron.daily |
Service configuration files enable or disable features of their respective services that if configured incorrectly can lead to insecure and vulnerable configurations. Therefore, service configuration files should have the correct access rights to prevent unauthorized changes. |
5.1.5 | Verify Owner on cron.weekly |
To properly set the owner of /etc/cron.weekly , run the command:
$ sudo chown root /etc/cron.weekly |
Service configuration files enable or disable features of their respective services that if configured incorrectly can lead to insecure and vulnerable configurations. Therefore, service configuration files should be owned by the correct user to prevent unauthorized changes. |
5.1.5 | Verify Permissions on cron.weekly |
To properly set the permissions of /etc/cron.weekly , run the command:
$ sudo chmod 0700 /etc/cron.weekly |
Service configuration files enable or disable features of their respective services that if configured incorrectly can lead to insecure and vulnerable configurations. Therefore, service configuration files should have the correct access rights to prevent unauthorized changes. |
5.1.5 | Verify Group Who Owns cron.weekly |
To properly set the group owner of /etc/cron.weekly , run the command:
$ sudo chgrp root /etc/cron.weekly |
Service configuration files enable or disable features of their respective services that if configured incorrectly can lead to insecure and vulnerable configurations. Therefore, service configuration files should be owned by the correct group to prevent unauthorized changes. |
5.1.6 | Verify Permissions on cron.monthly |
To properly set the permissions of /etc/cron.monthly , run the command:
$ sudo chmod 0700 /etc/cron.monthly |
Service configuration files enable or disable features of their respective services that if configured incorrectly can lead to insecure and vulnerable configurations. Therefore, service configuration files should have the correct access rights to prevent unauthorized changes. |
5.1.6 | Verify Group Who Owns cron.monthly |
To properly set the group owner of /etc/cron.monthly , run the command:
$ sudo chgrp root /etc/cron.monthly |
Service configuration files enable or disable features of their respective services that if configured incorrectly can lead to insecure and vulnerable configurations. Therefore, service configuration files should be owned by the correct group to prevent unauthorized changes. |
5.1.6 | Verify Owner on cron.monthly |
To properly set the owner of /etc/cron.monthly , run the command:
$ sudo chown root /etc/cron.monthly |
Service configuration files enable or disable features of their respective services that if configured incorrectly can lead to insecure and vulnerable configurations. Therefore, service configuration files should be owned by the correct user to prevent unauthorized changes. |
5.1.7 | Verify Owner on cron.d |
To properly set the owner of /etc/cron.d , run the command:
$ sudo chown root /etc/cron.d |
Service configuration files enable or disable features of their respective services that if configured incorrectly can lead to insecure and vulnerable configurations. Therefore, service configuration files should be owned by the correct user to prevent unauthorized changes. |
5.1.7 | Verify Group Who Owns cron.d |
To properly set the group owner of /etc/cron.d , run the command:
$ sudo chgrp root /etc/cron.d |
Service configuration files enable or disable features of their respective services that if configured incorrectly can lead to insecure and vulnerable configurations. Therefore, service configuration files should be owned by the correct group to prevent unauthorized changes. |
5.1.7 | Verify Permissions on cron.d |
To properly set the permissions of /etc/cron.d , run the command:
$ sudo chmod 0700 /etc/cron.d |
Service configuration files enable or disable features of their respective services that if configured incorrectly can lead to insecure and vulnerable configurations. Therefore, service configuration files should have the correct access rights to prevent unauthorized changes. |
5.1.8 | Verify Permissions on /etc/cron.allow file |
If /etc/cron.allow exists, it must have permissions 0600
or more restrictive.
To properly set the permissions of /etc/cron.allow , run the command:
$ sudo chmod 0600 /etc/cron.allow |
If the permissions of the cron.allow file are not set to 0600 or more restrictive, the possibility exists for an unauthorized user to view or edit sensitive information. |
5.1.8 | Ensure that /etc/cron.deny does not exist | The file /etc/cron.deny should not exist. Use /etc/cron.allow instead. | Access to cron should be restricted. It is easier to manage an allow list than a deny list. |
5.1.8 | Verify User Who Owns /etc/cron.allow file |
If /etc/cron.allow exists, it must be owned by root.
To properly set the owner of /etc/cron.allow , run the command:
$ sudo chown root /etc/cron.allow |
If the owner of the cron.allow file is not set to root, the possibility exists for an unauthorized user to view or edit sensitive information. |
5.1.8 | Verify Group Who Owns /etc/cron.allow file |
If /etc/cron.allow exists, it must be group-owned by root.
To properly set the group owner of /etc/cron.allow , run the command:
$ sudo chgrp root /etc/cron.allow |
If the owner of the cron.allow file is not set to root, the possibility exists for an unauthorized user to view or edit sensitive information. |
5.1.9 | Ensure that /etc/at.deny does not exist | The file /etc/at.deny should not exist. Use /etc/at.allow instead. | Access to at should be restricted. It is easier to manage an allow list than a deny list. |
5.2.1 | Install sudo Package |
The sudo package can be installed with the following command:
$ sudo yum install sudo |
sudo is a program designed to allow a system administrator to give limited root privileges to users and log root activity. The basic philosophy is to give as few privileges as possible but still allow system users to get their work done. |
5.2.2 | Allow Only SSH Protocol 2 |
Only SSH protocol version 2 connections should be
permitted. The default setting in
/etc/ssh/sshd_config is correct, and can be
verified by ensuring that the following
line appears:
Protocol 2 |
SSH protocol version 1 is an insecure implementation of the SSH protocol and has many well-known vulnerability exploits. Exploits of the SSH daemon could provide immediate root access to the system. |
5.2.2 | Ensure Only Users Logged In To Real tty Can Execute Sudo - sudo use_pty | The sudo use_pty tag, when specified, will only execute sudo commands from users logged in to a real tty. This should be enabled by making sure that the use_pty tag exists in /etc/sudoers configuration file or any sudo configuration snippets in /etc/sudoers.d/. | Requiring that sudo commands be run in a pseudo-terminal can prevent an attacker from retaining access to the user's terminal after the main program has finished executing. |
5.2.3 | Ensure Sudo Logfile Exists - sudo logfile | A custom log sudo file can be configured with the 'logfile' tag. This rule configures a sudo custom logfile at the default location suggested by CIS, which uses /var/log/sudo.log. | A sudo log file simplifies auditing of sudo commands. |
5.2.12 | Set SSH Client Alive Count Max to zero | The SSH server sends at most ClientAliveCountMax messages during a SSH session and waits for a response from the SSH client. The option ClientAliveInterval configures timeout after each ClientAliveCountMax message. If the SSH server does not receive a response from the client, then the connection is considered unresponsive and terminated. To ensure the SSH timeout occurs precisely when the ClientAliveInterval is set, set the ClientAliveCountMax to value of 0 in /etc/ssh/sshd_config: | This ensures a user login will be terminated as soon as the ClientAliveInterval is reached. |
5.2.14 | Limit Users' SSH Access |
By default, the SSH configuration allows any user with an account
to access the system. In order to specify the users that are allowed to login
via SSH and deny all other users, add or correct the following line in the
/etc/ssh/sshd_config file:
AllowUsers USER1 USER2Where USER1 and USER2 are valid user names. |
Specifying which accounts are allowed SSH access into the system reduces the possibility of unauthorized access to the system. |
5.2.15 | Enable SSH Warning Banner |
To enable the warning banner and ensure it is consistent
across the system, add or correct the following line in
/etc/ssh/sshd_config:
Banner /etc/issueAnother section contains information on how to create an appropriate system-wide warning banner. |
The warning message reinforces policy awareness during the logon process and facilitates possible legal action against attackers. Alternatively, systems whose ownership should not be obvious should ensure usage of a banner that does not provide easy attribution. |
5.3.1 | Verify Permissions on SSH Server config file |
To properly set the permissions of /etc/ssh/sshd_config , run the command:
$ sudo chmod 0600 /etc/ssh/sshd_config |
Service configuration files enable or disable features of their respective services that if configured incorrectly can lead to insecure and vulnerable configurations. Therefore, service configuration files should be owned by the correct group to prevent unauthorized changes. |
5.3.1 | Verify Owner on SSH Server config file |
To properly set the owner of /etc/ssh/sshd_config , run the command:
$ sudo chown root /etc/ssh/sshd_config |
Service configuration files enable or disable features of their respective services that if configured incorrectly can lead to insecure and vulnerable configurations. Therefore, service configuration files should be owned by the correct group to prevent unauthorized changes. |
5.3.1 | Verify Group Who Owns SSH Server config file |
To properly set the group owner of /etc/ssh/sshd_config , run the command:
$ sudo chgrp root /etc/ssh/sshd_config |
Service configuration files enable or disable features of their respective services that if configured incorrectly can lead to insecure and vulnerable configurations. Therefore, service configuration files should be owned by the correct group to prevent unauthorized changes. |
5.3.2 | Lock Accounts After Failed Password Attempts | This rule configures the system to lock out accounts after a number of incorrect login attempts using pam_faillock.so. pam_faillock.so module requires multiple entries in pam files. These entries must be carefully defined to work as expected. In order to avoid errors when manually editing these files, it is recommended to use the appropriate tools, such as authselect or authconfig, depending on the OS version. | By limiting the number of failed logon attempts, the risk of unauthorized system access via user password guessing, also known as brute-forcing, is reduced. Limits are imposed by locking the account. |
5.3.2 | Set Lockout Time for Failed Password Attempts | This rule configures the system to lock out accounts during a specified time period after a number of incorrect login attempts using pam_faillock.so. pam_faillock.so module requires multiple entries in pam files. These entries must be carefully defined to work as expected. In order to avoid any errors when manually editing these files, it is recommended to use the appropriate tools, such as authselect or authconfig, depending on the OS version. If unlock_time is set to 0, manual intervention by an administrator is required to unlock a user. This should be done using the faillock tool. | By limiting the number of failed logon attempts the risk of unauthorized system access via user password guessing, otherwise known as brute-forcing, is reduced. Limits are imposed by locking the account. |
5.3.3 | Verify Permissions on SSH Server Public *.pub Key Files |
To properly set the permissions of /etc/ssh/*.pub , run the command: $ sudo chmod 0644 /etc/ssh/*.pub |
If a public host key file is modified by an unauthorized user, the SSH service may be compromised. |
5.3.5 | Set LogLevel to INFO |
The INFO parameter specifices that record login and logout activity will be logged.
The default SSH configuration sets the log level to INFO. The appropriate configuration is used if no value is set for LogLevel. To explicitly specify the log level in SSH, add or correct the following line in /etc/ssh/sshd_config: LogLevel INFO |
SSH provides several logging levels with varying amounts of verbosity. DEBUG is specifically not recommended other than strictly for debugging SSH communications since it provides so much data that it is difficult to identify important security information. INFO level is the basic level that only records login activity of SSH users. In many situations, such as Incident Response, it is important to determine when a particular user was active on a system. The logout record can eliminate those users who disconnected, which helps narrow the field. |
5.3.5 | Set SSH Daemon LogLevel to VERBOSE |
The VERBOSE parameter configures the SSH daemon to record login and logout activity.
To specify the log level in
SSH, add or correct the following line in
/etc/ssh/sshd_config:
LogLevel VERBOSE |
SSH provides several logging levels with varying amounts of verbosity. DEBUG is specifically not recommended other than strictly for debugging SSH communications since it provides so much data that it is difficult to identify important security information. INFO or VERBOSE level is the basic level that only records login activity of SSH users. In many situations, such as Incident Response, it is important to determine when a particular user was active on a system. The logout record can eliminate those users who disconnected, which helps narrow the field. |
5.3.6 | Disable X11 Forwarding |
The X11Forwarding parameter provides the ability to tunnel X11 traffic
through the connection to enable remote graphic connections.
SSH has the capability to encrypt remote X11 connections when SSH's
X11Forwarding option is enabled.
The default SSH configuration disables X11Forwarding. The appropriate configuration is used if no value is set for X11Forwarding. To explicitly disable X11 Forwarding, add or correct the following line in /etc/ssh/sshd_config: X11Forwarding no |
Disable X11 forwarding unless there is an operational requirement to use X11 applications directly. There is a small risk that the remote X11 servers of users who are logged in via SSH with X11 forwarding could be compromised by other users on the X11 server. Note that even if X11 forwarding is disabled, users can always install their own forwarders. |
5.3.7 | Set SSH authentication attempt limit |
The MaxAuthTries parameter specifies the maximum number of authentication attempts
permitted per connection. Once the number of failures reaches half this value, additional failures are logged.
to set MaxAUthTries edit /etc/ssh/sshd_config as follows:
MaxAuthTries 4 |
Setting the MaxAuthTries parameter to a low number will minimize the risk of successful brute force attacks to the SSH server. |
5.3.8 | Disable SSH Support for .rhosts Files |
SSH can emulate the behavior of the obsolete rsh
command in allowing users to enable insecure access to their
accounts via .rhosts files.
The default SSH configuration disables support for .rhosts. The appropriate configuration is used if no value is set for IgnoreRhosts. To explicitly disable support for .rhosts files, add or correct the following line in /etc/ssh/sshd_config: IgnoreRhosts yes |
SSH trust relationships mean a compromise on one host can allow an attacker to move trivially to other hosts. |
5.3.9 | Disable Host-Based Authentication |
SSH's cryptographic host-based authentication is
more secure than .rhosts authentication. However, it is
not recommended that hosts unilaterally trust one another, even
within an organization.
The default SSH configuration disables host-based authentication. The appropriate configuration is used if no value is set for HostbasedAuthentication. To explicitly disable host-based authentication, add or correct the following line in /etc/ssh/sshd_config: HostbasedAuthentication no |
SSH trust relationships mean a compromise on one host can allow an attacker to move trivially to other hosts. |
5.3.10 | Disable SSH Root Login |
The root user should never be allowed to login to a
system directly over a network.
To disable root login via SSH, add or correct the following line in
/etc/ssh/sshd_config:
PermitRootLogin no |
Even though the communications channel may be encrypted, an additional layer of security is gained by extending the policy of not logging directly on as root. In addition, logging in with a user-specific account provides individual accountability of actions performed on the system and also helps to minimize direct attack attempts on root's password. |
5.3.11 | Disable SSH Access via Empty Passwords |
Disallow SSH login with empty passwords.
The default SSH configuration disables logins with empty passwords. The appropriate
configuration is used if no value is set for PermitEmptyPasswords.
To explicitly disallow SSH login from accounts with empty passwords, add or correct the following line in /etc/ssh/sshd_config: PermitEmptyPasswords noAny accounts with empty passwords should be disabled immediately, and PAM configuration should prevent users from being able to assign themselves empty passwords. |
Configuring this setting for the SSH daemon provides additional assurance that remote login via SSH will require a password, even in the event of misconfiguration elsewhere. |
5.3.12 | Do Not Allow SSH Environment Options |
Ensure that users are not able to override environment variables of the SSH daemon.
The default SSH configuration disables environment processing. The appropriate configuration is used if no value is set for PermitUserEnvironment. To explicitly disable Environment options, add or correct the following /etc/ssh/sshd_config: PermitUserEnvironment no |
SSH environment options potentially allow users to bypass access restriction in some configurations. |
5.3.13 | Use Only FIPS 140-2 Validated Ciphers |
Limit the ciphers to those algorithms which are FIPS-approved.
Counter (CTR) mode is also preferred over cipher-block chaining (CBC) mode.
The following line in /etc/ssh/sshd_config
demonstrates use of FIPS-approved ciphers:
Ciphers aes128-ctr,aes192-ctr,aes256-ctr,aes128-cbc,3des-cbc,aes192-cbc,aes256-cbcThe man page sshd_config(5) contains a list of supported ciphers. Only the following ciphers are FIPS 140-2 certified on Red Hat Enterprise Linux 7: - aes128-ctr - aes192-ctr - aes256-ctr - aes128-cbc - aes192-cbc - aes256-cbc - 3des-cbc - rijndael-cbc@lysator.liu.se Any combination of the above ciphers will pass this check. Official FIPS 140-2 paperwork for Red Hat Enterprise Linux 7 can be found at http://csrc.nist.gov/groups/STM/cmvp/documents/140-1/140sp/140sp2630.pdf The rule is parametrized to use the following ciphers: aes128-ctr,aes192-ctr,aes256-ctr,aes128-cbc,3des-cbc,aes192-cbc,aes256-cbc,rijndael-cbc@lysator.liu.se .
|
Unapproved mechanisms that are used for authentication to the cryptographic module are not verified and therefore
cannot be relied upon to provide confidentiality or integrity, and system data may be compromised.
Operating systems utilizing encryption are required to use FIPS-compliant mechanisms for authenticating to cryptographic modules. FIPS 140-2 is the current standard for validating that mechanisms used to access cryptographic modules utilize authentication that meets industry and government requirements. For government systems, this allows Security Levels 1, 2, 3, or 4 for use on Red Hat Enterprise Linux 7. |
5.3.14 | Use Only FIPS 140-2 Validated MACs |
Limit the MACs to those hash algorithms which are FIPS-approved.
The following line in /etc/ssh/sshd_config
demonstrates use of FIPS-approved MACs:
MACs hmac-sha2-512,hmac-sha2-256,hmac-sha1The man page sshd_config(5) contains a list of supported MACs. Only the following message authentication codes are FIPS 140-2 certified on Red Hat Enterprise Linux 7: - hmac-sha1 - hmac-sha2-256 - hmac-sha2-512 - hmac-sha1-etm@openssh.com - hmac-sha2-256-etm@openssh.com - hmac-sha2-512-etm@openssh.com Any combination of the above MACs will pass this check. Official FIPS 140-2 paperwork for Red Hat Enterprise Linux 7 can be found at http://csrc.nist.gov/groups/STM/cmvp/documents/140-1/140sp/140sp2630.pdf The rule is parametrized to use the following MACs: hmac-sha2-512,hmac-sha2-256,hmac-sha1,hmac-sha1-etm@openssh.com,hmac-sha2-256-etm@openssh.com,hmac-sha2-512-etm@openssh.com .
|
DoD Information Systems are required to use FIPS-approved cryptographic hash functions. The only SSHv2 hash algorithms meeting this requirement is SHA2. |
5.3.16 | Set SSH Client Alive Count Max | The SSH server sends at most ClientAliveCountMax messages during a SSH session and waits for a response from the SSH client. The option ClientAliveInterval configures timeout after each ClientAliveCountMax message. If the SSH server does not receive a response from the client, then the connection is considered unresponsive and terminated. For SSH earlier than v8.2, a ClientAliveCountMax value of 0 causes a timeout precisely when the ClientAliveInterval is set. Starting with v8.2, a value of 0 disables the timeout functionality completely. If the option is set to a number greater than 0, then the session will be disconnected after ClientAliveInterval * ClientAliveCountMax seconds without receiving a keep alive message. | This ensures a user login will be terminated as soon as the ClientAliveInterval is reached. |
5.3.16 | Set SSH Client Alive Interval |
SSH allows administrators to set a network responsiveness timeout interval.
After this interval has passed, the unresponsive client will be automatically logged out.
To set this timeout interval, edit the following line in /etc/ssh/sshd_config as follows: ClientAliveInterval 300 The timeout interval is given in seconds. For example, have a timeout of 10 minutes, set interval to 600. If a shorter timeout has already been set for the login shell, that value will preempt any SSH setting made in /etc/ssh/sshd_config. Keep in mind that some processes may stop SSH from correctly detecting that the user is idle. |
Terminating an idle ssh session within a short time period reduces the window of opportunity for unauthorized personnel to take control of a management session enabled on the console or console port that has been let unattended. |
5.3.17 | Ensure SSH LoginGraceTime is configured | The LoginGraceTime parameter to the SSH server specifies the time allowed for successful authentication to the SSH server. The longer the Grace period is the more open unauthenticated connections can exist. Like other session controls in this session the Grace Period should be limited to appropriate limits to ensure the service is available for needed access. | Setting the LoginGraceTime parameter to a low number will minimize the risk of successful brute force attacks to the SSH server. It will also limit the number of concurrent unauthenticated connections. |
5.3.19 | Enable PAM |
UsePAM Enables the Pluggable Authentication Module interface. If set to “yes” this will
enable PAM authentication using ChallengeResponseAuthentication and
PasswordAuthentication in addition to PAM account and session module processing for all
authentication types.
To enable PAM authentication, add or correct the following line in
/etc/ssh/sshd_config:
UsePAM yes |
When UsePAM is set to yes, PAM runs through account and session types properly. This is important if you want to restrict access to services based off of IP, time or other factors of the account. Additionally, you can make sure users inherit certain environment variables on login or disallow access to the server. |
5.3.20 | Disable SSH TCP Forwarding |
The AllowTcpForwarding parameter specifies whether TCP forwarding is permitted.
To disable TCP forwarding, add or correct the following line in
/etc/ssh/sshd_config:
AllowTcpForwarding no |
Leaving port forwarding enabled can expose the organization to security risks and back-doors. |
5.3.21 | Ensure SSH MaxStartups is configured |
The MaxStartups parameter specifies the maximum number of concurrent
unauthenticated connections to the SSH daemon. Additional connections will be
dropped until authentication succeeds or the LoginGraceTime expires for a
connection. To confgure MaxStartups, you should add or correct the following
line in the
/etc/ssh/sshd_config file:
MaxStartups 10:30:100CIS recommends a MaxStartups value of '10:30:60', or more restrictive where dictated by site policy. |
To protect a system from denial of service due to a large number of pending authentication connection attempts, use the rate limiting function of MaxStartups to protect availability of sshd logins and prevent overwhelming the daemon. |
5.3.22 | Set SSH MaxSessions limit |
The MaxSessions parameter specifies the maximum number of open sessions permitted
from a given connection. To set MaxSessions edit
/etc/ssh/sshd_config as follows: MaxSessions 10 |
To protect a system from denial of service due to a large number of concurrent sessions, use the rate limiting function of MaxSessions to protect availability of sshd logins and prevent overwhelming the daemon. |
5.4.1 | Ensure PAM Enforces Password Requirements - Minimum Lowercase Characters | The pam_pwquality module's lcredit parameter controls requirements for usage of lowercase letters in a password. When set to a negative number, any password will be required to contain that many lowercase characters. When set to a positive number, pam_pwquality will grant +1 additional length credit for each lowercase character. Modify the lcredit setting in /etc/security/pwquality.conf to require the use of a lowercase character in passwords. |
Use of a complex password helps to increase the time and resources required
to compromise the password. Password complexity, or strength, is a measure of
the effectiveness of a password in resisting attempts at guessing and brute-force
attacks.
Password complexity is one factor of several that determines how long it takes to crack a password. The more complex the password, the greater the number of possble combinations that need to be tested before the password is compromised. Requiring a minimum number of lowercase characters makes password guessing attacks more difficult by ensuring a larger search space. |
5.4.1 | Ensure PAM Enforces Password Requirements - Minimum Special Characters | The pam_pwquality module's ocredit= parameter controls requirements for usage of special (or "other") characters in a password. When set to a negative number, any password will be required to contain that many special characters. When set to a positive number, pam_pwquality will grant +1 additional length credit for each special character. Modify the ocredit setting in /etc/security/pwquality.conf to equal -1 to require use of a special character in passwords. |
Use of a complex password helps to increase the time and resources required
to compromise the password. Password complexity, or strength, is a measure of
the effectiveness of a password in resisting attempts at guessing and brute-force
attacks.
Password complexity is one factor of several that determines how long it takes to crack a password. The more complex the password, the greater the number of possible combinations that need to be tested before the password is compromised. Requiring a minimum number of special characters makes password guessing attacks more difficult by ensuring a larger search space. |
5.4.1 | Ensure PAM Enforces Password Requirements - Minimum Digit Characters | The pam_pwquality module's dcredit parameter controls requirements for usage of digits in a password. When set to a negative number, any password will be required to contain that many digits. When set to a positive number, pam_pwquality will grant +1 additional length credit for each digit. Modify the dcredit setting in /etc/security/pwquality.conf to require the use of a digit in passwords. |
Use of a complex password helps to increase the time and resources required
to compromise the password. Password complexity, or strength, is a measure of
the effectiveness of a password in resisting attempts at guessing and brute-force
attacks.
Password complexity is one factor of several that determines how long it takes to crack a password. The more complex the password, the greater the number of possible combinations that need to be tested before the password is compromised. Requiring digits makes password guessing attacks more difficult by ensuring a larger search space. |
5.4.1 | Ensure PAM Enforces Password Requirements - Authentication Retry Prompts Permitted Per-Session | To configure the number of retry prompts that are permitted per-session: Edit the pam_pwquality.so statement in /etc/pam.d/system-auth to show retry=3, or a lower value if site policy is more restrictive. The DoD requirement is a maximum of 3 prompts per session. | Setting the password retry prompts that are permitted on a per-session basis to a low value requires some software, such as SSH, to re-connect. This can slow down and draw additional attention to some types of password-guessing attacks. Note that this is different from account lockout, which is provided by the pam_faillock module. |
5.4.1 | Ensure PAM Enforces Password Requirements - Minimum Length | The pam_pwquality module's minlen parameter controls requirements for minimum characters required in a password. Add minlen=15 after pam_pwquality to set minimum password length requirements. |
The shorter the password, the lower the number of possible combinations
that need to be tested before the password is compromised.
Password complexity, or strength, is a measure of the effectiveness of a password in resisting attempts at guessing and brute-force attacks. Password length is one factor of several that helps to determine strength and how long it takes to crack a password. Use of more characters in a password helps to exponentially increase the time and/or resources required to compromise the password. |
5.4.1 | Ensure PAM Enforces Password Requirements - Minimum Uppercase Characters | The pam_pwquality module's ucredit= parameter controls requirements for usage of uppercase letters in a password. When set to a negative number, any password will be required to contain that many uppercase characters. When set to a positive number, pam_pwquality will grant +1 additional length credit for each uppercase character. Modify the ucredit setting in /etc/security/pwquality.conf to require the use of an uppercase character in passwords. |
Use of a complex password helps to increase the time and resources required to compromise the password.
Password complexity, or strength, is a measure of the effectiveness of a password in resisting attempts
at guessing and brute-force attacks.
Password complexity is one factor of several that determines how long it takes to crack a password. The more complex the password, the greater the number of possible combinations that need to be tested before the password is compromised. |
5.4.1 | Ensure PAM Enforces Password Requirements - Minimum Different Categories |
The pam_pwquality module's minclass parameter controls
requirements for usage of different character classes, or types, of character
that must exist in a password before it is considered valid. For example,
setting this value to three (3) requires that any password must have characters
from at least three different categories in order to be approved. The default
value is zero (0), meaning there are no required classes. There are four
categories available:
* Upper-case characters * Lower-case characters * Digits * Special characters (for example, punctuation)Modify the minclass setting in /etc/security/pwquality.conf entry to require 3 differing categories of characters when changing passwords. |
Use of a complex password helps to increase the time and resources required to compromise the password.
Password complexity, or strength, is a measure of the effectiveness of a password in resisting attempts
at guessing and brute-force attacks.
Password complexity is one factor of several that determines how long it takes to crack a password. The more complex the password, the greater the number of possible combinations that need to be tested before the password is compromised. Requiring a minimum number of character categories makes password guessing attacks more difficult by ensuring a larger search space. |
5.4.3 | Set PAM''s Password Hashing Algorithm |
The PAM system service can be configured to only store encrypted
representations of passwords. In "/etc/pam.d/system-auth", the
password section of the file controls which PAM modules execute
during a password change. Set the pam_unix.so module in the
password section to include the argument sha512, as shown
below:
password sufficient pam_unix.so sha512 other arguments... This will help ensure when local users change their passwords, hashes for the new passwords will be generated using the SHA-512 algorithm. This is the default. |
Passwords need to be protected at all times, and encryption is the standard
method for protecting passwords. If passwords are not encrypted, they can
be plainly read (i.e., clear text) and easily compromised. Passwords that
are encrypted with a weak algorithm are no more protected than if they are
kepy in plain text.
This setting ensures user and group account administration utilities are configured to store only encrypted representations of passwords. Additionally, the crypt_style configuration option ensures the use of a strong hashing algorithm that makes password cracking attacks more difficult. |
5.4.3 | Set PAM''s Password Hashing Algorithm - password-auth |
The PAM system service can be configured to only store encrypted
representations of passwords. In
/etc/pam.d/password-auth,
the
password section of the file controls which PAM modules execute
during a password change. Set the pam_unix.so module in the
password section to include the argument sha512, as shown
below:
password sufficient pam_unix.so sha512 other arguments... This will help ensure when local users change their passwords, hashes for the new passwords will be generated using the SHA-512 algorithm. This is the default. |
Passwords need to be protected at all times, and encryption is the standard
method for protecting passwords. If passwords are not encrypted, they can
be plainly read (i.e., clear text) and easily compromised. Passwords that
are encrypted with a weak algorithm are no more protected than if they are
kepy in plain text.
This setting ensures user and group account administration utilities are configured to store only encrypted representations of passwords. Additionally, the crypt_style configuration option ensures the use of a strong hashing algorithm that makes password cracking attacks more difficult. |
5.4.4 | Limit Password Reuse | Do not allow users to reuse recent passwords. This can be accomplished by using the remember option for the pam_unix or pam_pwhistory PAM modules. | Preventing re-use of previous passwords helps ensure that a compromised password is not re-used by a user. |
5.4.4 | Limit Password Reuse: system-auth |
Do not allow users to reuse recent passwords. This can be accomplished by using the
remember option for the pam_pwhistory PAM module.
In the file /etc/pam.d/system-auth, make sure the parameter remember is present and it has a value equal to or greater than 5 For example: password requisite pam_pwhistory.so use_authtok remember=5 |
Preventing re-use of previous passwords helps ensure that a compromised password is not re-used by a user. |
5.4.4 | Limit Password Reuse: password-auth |
Do not allow users to reuse recent passwords. This can be accomplished by using the
remember option for the pam_pwhistory PAM module.
In the file /etc/pam.d/password-auth, make sure the parameter remember is present and it has a value equal to or greater than 5 For example: password requisite pam_pwhistory.so use_authtok remember=5 |
Preventing re-use of previous passwords helps ensure that a compromised password is not re-used by a user. |
5.5 | Direct root Logins Not Allowed |
To further limit access to the root account, administrators
can disable root logins at the console by editing the /etc/securetty file.
This file lists all devices the root user is allowed to login to. If the file does
not exist at all, the root user can login through any communication device on the
system, whether via the console or via a raw network interface. This is dangerous
as user can login to the system as root via Telnet, which sends the password in
plain text over the network. By default, Red Hat Enterprise Linux 7's
/etc/securetty file only allows the root user to login at the console
physically attached to the system. To prevent root from logging in, remove the
contents of this file. To prevent direct root logins, remove the contents of this
file by typing the following command:
$ sudo echo > /etc/securetty |
Disabling direct root logins ensures proper accountability and multifactor authentication to privileged accounts. Users will first login, then escalate to privileged (root) access via su / sudo. This is required for FISMA Low and FISMA Moderate systems. |
5.5.1.1 | Set Password Maximum Age |
To specify password maximum age for new accounts,
edit the file /etc/login.defs
and add or correct the following line:
PASS_MAX_DAYS 60A value of 180 days is sufficient for many environments. The DoD requirement is 60. The profile requirement is 60. |
Any password, no matter how complex, can eventually be cracked. Therefore, passwords
need to be changed periodically. If the operating system does not limit the lifetime
of passwords and force users to change their passwords, there is the risk that the
operating system passwords could be compromised.
Setting the password maximum age ensures users are required to periodically change their passwords. Requiring shorter password lifetimes increases the risk of users writing down the password in a convenient location subject to physical compromise. |
5.5.1.2 | Set Password Minimum Age |
To specify password minimum age for new accounts,
edit the file /etc/login.defs
and add or correct the following line:
PASS_MIN_DAYS 7A value of 1 day is considered sufficient for many environments. The DoD requirement is 1. The profile requirement is 7. |
Enforcing a minimum password lifetime helps to prevent repeated password
changes to defeat the password reuse or history enforcement requirement. If
users are allowed to immediately and continually change their password,
then the password could be repeatedly changed in a short period of time to
defeat the organization's policy regarding password reuse.
Setting the minimum password age protects against users cycling back to a favorite password after satisfying the password reuse requirement. |
5.5.1.3 | Set Password Warning Age |
To specify how many days prior to password
expiration that a warning will be issued to users,
edit the file /etc/login.defs and add or correct
the following line:
PASS_WARN_AGE 7The DoD requirement is 7. The profile requirement is 7. |
Setting the password warning age enables users to make the change at a practical time. |
5.5.1.4 | Set Account Expiration Following Inactivity |
To specify the number of days after a password expires (which
signifies inactivity) until an account is permanently disabled, add or correct
the following line in /etc/default/useradd:
INACTIVE=35If a password is currently on the verge of expiration, then 35 day(s) remain(s) until the account is automatically disabled. However, if the password will not expire for another 60 days, then 60 days plus 35 day(s) could elapse until the account would be automatically disabled. See the useradd man page for more information. |
Inactive identifiers pose a risk to systems and applications because attackers may exploit an inactive identifier and potentially obtain undetected access to the system. Disabling inactive accounts ensures that accounts which may not have been responsibly removed are not available to attackers who may have compromised their credentials. Owners of inactive accounts will not notice if unauthorized access to their user account has been obtained. |
5.5.2 | Ensure that System Accounts Do Not Run a Shell Upon Login |
Some accounts are not associated with a human user of the system, and exist to
perform some administrative function. Should an attacker be able to log into
these accounts, they should not be granted access to a shell.
The login shell for each local account is stored in the last field of each line in /etc/passwd. System accounts are those user accounts with a user ID less than UID_MIN, where value of UID_MIN directive is set in /etc/login.defs configuration file. In the default configuration UID_MIN is set to 1000, thus system accounts are those user accounts with a user ID less than 1000. The user ID is stored in the third field. If any system account SYSACCT (other than root) has a login shell, disable it with the command: $ sudo usermod -s /sbin/nologin SYSACCT |
Ensuring shells are not given to system accounts upon login makes it more difficult for attackers to make use of system accounts. |
5.5.3 | Verify Root Has A Primary GID 0 | The root user should have a primary group of 0. | To help ensure that root-owned files are not inadvertently exposed to other users. |
5.5.4 | Set Interactive Session Timeout |
Setting the TMOUT option in /etc/profile ensures that
all user sessions will terminate based on inactivity.
The value of TMOUT should be exported and read only.
The TMOUT
setting in a file loaded by /etc/profileor /etc/bashrc, e.g.
/etc/profile.d/tmout.sh should read as follows:
declare -xr TMOUT=600 |
Terminating an idle session within a short time period reduces the window of opportunity for unauthorized personnel to take control of a management session enabled on the console or console port that has been left unattended. |
5.5.5 | Ensure the Default Bash Umask is Set Correctly |
To ensure the default umask for users of the Bash shell is set properly,
add or correct the umask setting in /etc/bashrc to read
as follows:
umask 027 |
The umask value influences the permissions assigned to files when they are created. A misconfigured umask value could result in files with excessive permissions that can be read or written to by unauthorized users. |
5.5.5 | Ensure the Default Umask is Set Correctly in login.defs |
To ensure the default umask controlled by /etc/login.defs is set properly,
add or correct the UMASK setting in /etc/login.defs to read as follows:
UMASK 027 |
The umask value influences the permissions assigned to files when they are created. A misconfigured umask value could result in files with excessive permissions that can be read and written to by unauthorized users. |
5.5.5 | Ensure the Default Umask is Set Correctly in /etc/profile |
To ensure the default umask controlled by /etc/profile is set properly,
add or correct the umask setting in /etc/profile to read as follows:
umask 027 |
The umask value influences the permissions assigned to files when they are created. A misconfigured umask value could result in files with excessive permissions that can be read or written to by unauthorized users. |
5.7 | Enforce usage of pam_wheel for su authentication |
To ensure that only users who are members of the wheel group can
run commands with altered privileges through the su command, make
sure that the following line exists in the file /etc/pam.d/su:
auth required pam_wheel.so use_uid |
The su program allows to run commands with a substitute user and group ID. It is commonly used to run commands as the root user. Limiting access to such command is considered a good security practice. |
6.1.1 | Verify File Hashes with RPM |
Without cryptographic integrity protections, system
executables and files can be altered by unauthorized users without
detection.
The RPM package management system can check the hashes of
installed software packages, including many that are important to system
security.
To verify that the cryptographic hash of system files and commands matches vendor
values, run the following command to list which files on the system
have hashes that differ from what is expected by the RPM database:
$ rpm -Va --noconfig | grep '^..5'A "c" in the second column indicates that a file is a configuration file, which may appropriately be expected to change. If the file was not expected to change, investigate the cause of the change using audit logs or other means. The package can then be reinstalled to restore the file. Run the following command to determine which package owns the file: $ rpm -qf FILENAMEThe package can be reinstalled from a yum repository using the command: $ sudo yum reinstall PACKAGENAMEAlternatively, the package can be reinstalled from trusted media using the command: $ sudo rpm -Uvh PACKAGENAME |
The hashes of important files like system executables should match the information given by the RPM database. Executables with erroneous hashes could be a sign of nefarious activity on the system. |
6.1.2 | Verify Group Who Owns passwd File |
To properly set the group owner of /etc/passwd , run the command: $ sudo chgrp root /etc/passwd |
The /etc/passwd file contains information about the users that are configured on the system. Protection of this file is critical for system security. |
6.1.2 | Verify User Who Owns passwd File |
To properly set the owner of /etc/passwd , run the command: $ sudo chown root /etc/passwd |
The /etc/passwd file contains information about the users that are configured on the system. Protection of this file is critical for system security. |
6.1.2 | Verify Permissions on passwd File |
To properly set the permissions of /etc/passwd , run the command:
$ sudo chmod 0644 /etc/passwd |
If the /etc/passwd file is writable by a group-owner or the world the risk of its compromise is increased. The file contains the list of accounts on the system and associated information, and protection of this file is critical for system security. |
6.1.3 | Verify Permissions on Backup passwd File |
To properly set the permissions of /etc/passwd- , run the command:
$ sudo chmod 0644 /etc/passwd- |
The /etc/passwd- file is a backup file of /etc/passwd, and as such, it contains information about the users that are configured on the system. Protection of this file is critical for system security. |
6.1.3 | Verify User Who Owns Backup passwd File |
To properly set the owner of /etc/passwd- , run the command: $ sudo chown root /etc/passwd- |
The /etc/passwd- file is a backup file of /etc/passwd, and as such, it contains information about the users that are configured on the system. Protection of this file is critical for system security. |
6.1.3 | Verify Group Who Owns Backup passwd File |
To properly set the group owner of /etc/passwd- , run the command: $ sudo chgrp root /etc/passwd- |
The /etc/passwd- file is a backup file of /etc/passwd, and as such, it contains information about the users that are configured on the system. Protection of this file is critical for system security. |
6.1.4 | Verify Group Who Owns shadow File |
To properly set the group owner of /etc/shadow , run the command: $ sudo chgrp root /etc/shadow |
The /etc/shadow file stores password hashes. Protection of this file is critical for system security. |
6.1.4 | Verify User Who Owns shadow File |
To properly set the owner of /etc/shadow , run the command: $ sudo chown root /etc/shadow |
The /etc/shadow file contains the list of local system accounts and stores password hashes. Protection of this file is critical for system security. Failure to give ownership of this file to root provides the designated owner with access to sensitive information which could weaken the system security posture. |
6.1.4 | Verify Permissions on shadow File |
To properly set the permissions of /etc/shadow , run the command:
$ sudo chmod 0000 /etc/shadow |
The /etc/shadow file contains the list of local system accounts and stores password hashes. Protection of this file is critical for system security. Failure to give ownership of this file to root provides the designated owner with access to sensitive information which could weaken the system security posture. |
6.1.5 | Verify Permissions on Backup shadow File |
To properly set the permissions of /etc/shadow- , run the command:
$ sudo chmod 0000 /etc/shadow- |
The /etc/shadow- file is a backup file of /etc/shadow, and as such, it contains the list of local system accounts and password hashes. Protection of this file is critical for system security. |
6.1.5 | Verify User Who Owns Backup shadow File |
To properly set the group owner of /etc/shadow- , run the command: $ sudo chgrp root /etc/shadow- |
The /etc/shadow- file is a backup file of /etc/shadow, and as such, it contains the list of local system accounts and password hashes. Protection of this file is critical for system security. |
6.1.5 | Verify Group Who Owns Backup shadow File |
To properly set the owner of /etc/shadow- , run the command: $ sudo chown root /etc/shadow- |
The /etc/shadow- file is a backup file of /etc/shadow, and as such, it contains the list of local system accounts and password hashes. Protection of this file is critical for system security. |
6.1.6 | Verify Group Who Owns Backup gshadow File |
To properly set the group owner of /etc/gshadow- , run the command: $ sudo chgrp root /etc/gshadow- |
The /etc/gshadow- file is a backup of /etc/gshadow, and as such, it contains group password hashes. Protection of this file is critical for system security. |
6.1.6 | Verify Permissions on Backup gshadow File |
To properly set the permissions of /etc/gshadow- , run the command:
$ sudo chmod 0000 /etc/gshadow- |
The /etc/gshadow- file is a backup of /etc/gshadow, and as such, it contains group password hashes. Protection of this file is critical for system security. |
6.1.6 | Verify User Who Owns Backup gshadow File |
To properly set the owner of /etc/gshadow- , run the command: $ sudo chown root /etc/gshadow- |
The /etc/gshadow- file is a backup of /etc/gshadow, and as such, it contains group password hashes. Protection of this file is critical for system security. |
6.1.7 | Verify Permissions on gshadow File |
To properly set the permissions of /etc/gshadow , run the command:
$ sudo chmod 0000 /etc/gshadow |
The /etc/gshadow file contains group password hashes. Protection of this file is critical for system security. |
6.1.7 | Verify Group Who Owns gshadow File |
To properly set the group owner of /etc/gshadow , run the command: $ sudo chgrp root /etc/gshadow |
The /etc/gshadow file contains group password hashes. Protection of this file is critical for system security. |
6.1.7 | Verify User Who Owns gshadow File |
To properly set the owner of /etc/gshadow , run the command: $ sudo chown root /etc/gshadow |
The /etc/gshadow file contains group password hashes. Protection of this file is critical for system security. |
6.1.8 | Verify User Who Owns group File |
To properly set the owner of /etc/group , run the command: $ sudo chown root /etc/group |
The /etc/group file contains information regarding groups that are configured on the system. Protection of this file is important for system security. |
6.1.8 | Verify Permissions on group File |
To properly set the permissions of /etc/passwd , run the command:
$ sudo chmod 0644 /etc/passwd |
The /etc/group file contains information regarding groups that are configured on the system. Protection of this file is important for system security. |
6.1.8 | Verify Group Who Owns group File |
To properly set the group owner of /etc/group , run the command: $ sudo chgrp root /etc/group |
The /etc/group file contains information regarding groups that are configured on the system. Protection of this file is important for system security. |
6.1.9 | Verify User Who Owns Backup group File |
To properly set the owner of /etc/group- , run the command: $ sudo chown root /etc/group- |
The /etc/group- file is a backup file of /etc/group, and as such, it contains information regarding groups that are configured on the system. Protection of this file is important for system security. |
6.1.9 | Verify Permissions on Backup group File |
To properly set the permissions of /etc/group- , run the command:
$ sudo chmod 0644 /etc/group- |
The /etc/group- file is a backup file of /etc/group, and as such, it contains information regarding groups that are configured on the system. Protection of this file is important for system security. |
6.1.9 | Verify Group Who Owns Backup group File |
To properly set the group owner of /etc/group- , run the command: $ sudo chgrp root /etc/group- |
The /etc/group- file is a backup file of /etc/group, and as such, it contains information regarding groups that are configured on the system. Protection of this file is important for system security. |
6.1.10 | Ensure No World-Writable Files Exist | It is generally a good idea to remove global (other) write access to a file when it is discovered. However, check with documentation for specific applications before making changes. Also, monitor for recurring world-writable files, as these may be symptoms of a misconfigured application or user account. Finally, this applies to real files and not virtual files that are a part of pseudo file systems such as sysfs or procfs. | Data in world-writable files can be modified by any user on the system. In almost all circumstances, files can be configured using a combination of user and group permissions to support whatever legitimate access is needed without the risk caused by world-writable files. |
6.1.11 | Ensure All Files Are Owned by a User |
If any files are not owned by a user, then the
cause of their lack of ownership should be investigated.
Following this, the files should be deleted or assigned to an
appropriate user. The following command will discover and print
any files on local partitions which do not belong to a valid user:
$ df --local -P | awk {'if (NR!=1) print $6'} | sudo xargs -I '{}' find '{}' -xdev -nouserTo search all filesystems on a system including network mounted filesystems the following command can be run manually for each partition: $ sudo find PARTITION -xdev -nouser |
Unowned files do not directly imply a security problem, but they are generally a sign that something is amiss. They may be caused by an intruder, by incorrect software installation or draft software removal, or by failure to remove all files belonging to a deleted account. The files should be repaired so they will not cause problems when accounts are created in the future, and the cause should be discovered and addressed. |
6.1.12 | Ensure All Files Are Owned by a Group |
If any files are not owned by a group, then the
cause of their lack of group-ownership should be investigated.
Following this, the files should be deleted or assigned to an
appropriate group. The following command will discover and print
any files on local partitions which do not belong to a valid group:
$ df --local -P | awk '{if (NR!=1) print $6}' | sudo xargs -I '{}' find '{}' -xdev -nogroupTo search all filesystems on a system including network mounted filesystems the following command can be run manually for each partition: $ sudo find PARTITION -xdev -nogroup |
Unowned files do not directly imply a security problem, but they are generally a sign that something is amiss. They may be caused by an intruder, by incorrect software installation or draft software removal, or by failure to remove all files belonging to a deleted account. The files should be repaired so they will not cause problems when accounts are created in the future, and the cause should be discovered and addressed. |
6.1.13 | Ensure All SUID Executables Are Authorized | The SUID (set user id) bit should be set only on files that were installed via authorized means. A straightforward means of identifying unauthorized SUID files is determine if any were not installed as part of an RPM package, which is cryptographically verified. Investigate the origin of any unpackaged SUID files. This configuration check considers authorized SUID files which were installed via RPM. It is assumed that when an individual has sudo access to install an RPM and all packages are signed with an organizationally-recognized GPG key, the software should be considered an approved package on the system. Any SUID file not deployed through an RPM will be flagged for further review. | Executable files with the SUID permission run with the privileges of the owner of the file. SUID files of uncertain provenance could allow for unprivileged users to elevate privileges. The presence of these files should be strictly controlled on the system. |
6.1.14 | Ensure All SGID Executables Are Authorized | The SGID (set group id) bit should be set only on files that were installed via authorized means. A straightforward means of identifying unauthorized SGID files is determine if any were not installed as part of an RPM package, which is cryptographically verified. Investigate the origin of any unpackaged SGID files. This configuration check considers authorized SGID files which were installed via RPM. It is assumed that when an individual has sudo access to install an RPM and all packages are signed with an organizationally-recognized GPG key, the software should be considered an approved package on the system. Any SGID file not deployed through an RPM will be flagged for further review. | Executable files with the SGID permission run with the privileges of the owner of the file. SGID files of uncertain provenance could allow for unprivileged users to elevate privileges. The presence of these files should be strictly controlled on the system. |
6.2.1 | Verify All Account Password Hashes are Shadowed | If any password hashes are stored in /etc/passwd (in the second field, instead of an x or *), the cause of this misconfiguration should be investigated. The account should have its password reset and the hash should be properly stored, or the account should be deleted entirely. | The hashes for all user account passwords should be stored in the file /etc/shadow and never in /etc/passwd, which is readable by all users. |
6.2.2 | Ensure there are no legacy + NIS entries in /etc/passwd | The + character in /etc/passwd file marks a place where entries from a network information service (NIS) should be directly inserted. | Using this method to include entries into /etc/passwd is considered legacy and should be avoided. These entries may provide a way for an attacker to gain access to the system. |
6.2.3 | Ensure there are no legacy + NIS entries in /etc/shadow | The + character in /etc/shadow file marks a place where entries from a network information service (NIS) should be directly inserted. | Using this method to include entries into /etc/shadow is considered legacy and should be avoided. These entries may provide a way for an attacker to gain access to the system. |
6.2.3 | All GIDs referenced in /etc/passwd must be defined in /etc/group | Add a group to the system for each GID referenced without a corresponding group. | If a user is assigned the Group Identifier (GID) of a group not existing on the system, and a group with the Group Identifier (GID) is subsequently created, the user may have unintended rights to any files associated with the group. |
6.2.5 | Ensure All Accounts on the System Have Unique Names |
Ensure accounts on the system have unique names.
To ensure all accounts have unique names, run the following command:
$ sudo getent passwd | awk -F: '{ print $1}' | uniq -dIf a username is returned, change or delete the username. |
Unique usernames allow for accountability on the system. |
6.2.6 | Ensure All Groups on the System Have Unique Group Names | Change the group name or delete groups, so each has a unique name. | To assure accountability and prevent unauthenticated access, groups must be identified uniquely to prevent potential misuse and compromise of the system. |
6.2.7 | Ensure All Groups on the System Have Unique Group ID | Change the group name or delete groups, so each has a unique id. | To assure accountability and prevent unauthenticated access, groups must be identified uniquely to prevent potential misuse and compromise of the system. |
6.2.7 | Ensure All Accounts on the System Have Unique User IDs | Change user IDs (UIDs), or delete accounts, so each has a unique name. | To assure accountability and prevent unauthenticated access, interactive users must be identified and authenticated to prevent potential misuse and compromise of the system. |
6.2.9 | Verify Only Root Has UID 0 |
If any account other than root has a UID of 0, this misconfiguration should
be investigated and the accounts other than root should be removed or have
their UID changed.
If the account is associated with system commands or applications the UID should be changed to one greater than "0" but less than "1000." Otherwise assign a UID greater than "1000" that has not already been assigned. |
An account has root authority if it has a UID of 0. Multiple accounts with a UID of 0 afford more opportunity for potential intruders to guess a password for a privileged account. Proper configuration of sudo is recommended to afford multiple system administrators access to root privileges in an accountable manner. |
6.2.10 | Ensure that Root's Path Does Not Include World or Group-Writable Directories |
For each element in root's path, run:
# ls -ld DIRand ensure that write permissions are disabled for group and other. |
Such entries increase the risk that root could execute code provided by unprivileged users, and potentially malicious code. |
6.2.10 | Ensure that Root's Path Does Not Include Relative Paths or Null Directories |
Ensure that none of the directories in root's path is equal to a single
. character, or
that it contains any instances that lead to relative path traversal, such as
.. or beginning a path without the slash (/) character.
Also ensure that there are no "empty" elements in the path, such as in these examples:
PATH=:/bin PATH=/bin: PATH=/bin::/sbinThese empty elements have the same effect as a single . character. |
Including these entries increases the risk that root could execute code from an untrusted location. |
6.2.11 | All Interactive Users Home Directories Must Exist |
Create home directories to all interactive users that currently do not
have a home directory assigned. Use the following commands to create the user
home directory assigned in /etc/passwd:
$ sudo mkdir /home/USER |
If a local interactive user has a home directory defined that does not exist, the user may be given access to the / directory as the current working directory upon logon. This could create a Denial of Service because the user would not be able to access their logon configuration files, and it may give them visibility to system files they normally would not be able to access. |
6.2.12 | All Interactive User Home Directories Must Be Owned By The Primary User |
Change the owner of interactive users home directories to that correct
owner. To change the owner of a interactive users home directory, use
the following command:
$ sudo chown USER /home/USERThis rule ensures every home directory related to an interactive user is owned by an interactive user. It also ensures that interactive users are owners of one and only one home directory. |
If a local interactive user does not own their home directory, unauthorized users could access or modify the user's files, and the users may not be able to access their own files. |
6.2.13 | All Interactive User Home Directories Must Have mode 0750 Or Less Permissive |
Change the mode of interactive users home directories to 0750. To
change the mode of interactive users home directory, use the
following command:
$ sudo chmod 0750 /home/USER |
Excessive permissions on local interactive user home directories may allow unauthorized access to user files by other users. |
6.2.14 | Remove Rsh Trust Files |
The files /etc/hosts.equiv and ~/.rhosts (in
each user's home directory) list remote hosts and users that are trusted by the
local system when using the rshd daemon.
To remove these files, run the following command to delete them from any
location:
$ sudo rm /etc/hosts.equiv $ rm ~/.rhosts |
This action is only meaningful if .rhosts support is permitted through PAM. Trust files are convenient, but when used in conjunction with the R-services, they can allow unauthenticated access to a system. |
6.2.16 | Verify No netrc Files Exist | The .netrc files contain login information used to auto-login into FTP servers and reside in the user's home directory. These files may contain unencrypted passwords to remote FTP servers making them susceptible to access by unauthorized users and should not be used. Any .netrc files should be removed. | Unencrypted passwords for remote FTP servers may be stored in .netrc files. |