4.1.3.13 Ensure file deletion events by users are collected

Information

Monitor the use of system calls associated with the deletion or renaming of files and file attributes. This configuration statement sets up monitoring for:

unlink - remove a file

unlinkat - remove a file attribute

rename - rename a file

renameat rename a file attribute system calls and tags them with the identifier 'delete'.

Rationale:

Monitoring these calls from non-privileged users could provide a system administrator with evidence that inappropriate removal of files and file attributes associated with protected files is occurring. While this audit option will look at all events, system administrators will want to look for specific privileged files that are being deleted or altered.

Solution

Create audit rules

Edit or create a file in the /etc/audit/rules.d/ directory, ending in .rules extension, with the relevant rules to monitor file deletion events by users.

64 Bit systems

Example:

# {
UID_MIN=$(awk '/^s*UID_MIN/{print $2}' /etc/login.defs)
[ -n '${UID_MIN}' ] && printf '
-a always,exit -F arch=b64 -S rename,unlink,unlinkat,renameat -F auid>=${UID_MIN} -F auid!=unset -F key=delete
-a always,exit -F arch=b32 -S rename,unlink,unlinkat,renameat -F auid>=${UID_MIN} -F auid!=unset -F key=delete
' >> /etc/audit/rules.d/50-delete.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.

See Also

https://workbench.cisecurity.org/files/3807