Detections
Analytics
4.1.3.10 Ensure successful file system mounts are collected
Information
Monitor the use of the mount system call. The mount (and umount ) system call controls the mounting and unmounting of file systems. The parameters below configure the system to create an audit record when the mount system call is used by a non-privileged userRationale:
It is highly unusual for a non privileged user to mount file systems to the system. While tracking mount commands gives the system administrator evidence that external media may have been mounted (based on a review of the source of the mount and confirming it's an external media type), it does not conclusively indicate that data was exported to the media. System administrators who wish to determine if data were exported, would also have to track successful open, creat and truncate system calls requiring write access to a file under the mount point of the external media file system. This could give a fair indication that a write occurred. The only way to truly prove it, would be to track successful writes to the external media. Tracking write system calls could quickly fill up the audit log and is not recommended. Recommendations on configuration options to track data export to media is beyond the scope of this document.
Solution
Create audit rulesEdit or create a file in the /etc/audit/rules.d/ directory, ending in .rules extension, with the relevant rules to monitor successful file system mounts.
64 Bit systems
Example:
# {
UID_MIN=$(awk '/^s*UID_MIN/{print $2}' /etc/login.defs)
[ -n '${UID_MIN}' ] && printf '
-a always,exit -F arch=b32 -S mount -F auid>=$UID_MIN -F auid!=unset -k mounts
-a always,exit -F arch=b64 -S mount -F auid>=$UID_MIN -F auid!=unset -k mounts
' >> /etc/audit/rules.d/50-mounts.rules || printf 'ERROR: Variable 'UID_MIN' is unset.
'
}
Load audit rules
Merge and load the rules into active configuration:
# augenrules --load
Check if reboot is required.
# if [[ $(auditctl -s | grep 'enabled') =~ '2' ]]; then printf 'Reboot required to load rules
'; fi
32 Bit systems
Follow the same procedures as for 64 bit systems and ignore any entries with b64.
Additional Information:
Potential reboot required
If the auditing configuration is locked (-e 2), then augenrules will not warn in any way that rules could not be loaded into the running configuration. A system reboot will be required to load the rules into the running configuration.
System call structure
For performance (man 7 audit.rules) reasons it is preferable to have all the system calls on one line. However, your configuration may have them on one line each or some other combination. This is important to understand for both the auditing and remediation sections as the examples given are optimized for performance as per the man page.
NIST SP 800-53 Rev. 5:
CM-6
See Also
Item Details
Audit Name: CIS Debian Linux 11 Server L2 v.1.0.0
References: CSCv7|6.3
Plugin: Unix
Control ID: 906f46451711470074849dfda553c07c49a8fd4a25969f7b692b06b979fb433e