Detections
Analytics

6.2.3.21 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 user

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

- Add the audit rule(s) for the mount system call. The procedure adds a rule for each audit ABI (b64/b32) the running kernel supports and skips any unsupported ABI or system call, so augenrules --load does not error. Run:

#!/usr/bin/env bash

{
 UID_MIN="$(awk '/^[[:space:]]*UID_MIN/{print $2}' /etc/login.defs)"
 for ARCH in b64 b32; do
 CALLS=""; for C in mount; do ausyscall "$ARCH" "$C" >/dev/null 2>&1 && CALLS="${CALLS:+$CALLS,}$C"; done
 [ -n "$CALLS" ] && printf '%s\n' "-a always,exit -F arch=$ARCH -S $CALLS -F auid>=$UID_MIN -F auid!=unset -k mounts"
 done >> /etc/audit/rules.d/50-mounts.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\n"; fi

See Also

https://workbench.cisecurity.org/benchmarks/27892

Item Details

Category: AUDIT AND ACCOUNTABILITY

References: 800-53|AU-3, 800-53|AU-3(1), 800-53|AU-7, 800-53|AU-12, 800-53|AU-12a., CSCv7|6.3

Plugin: Unix

Control ID: 9ac3700d1ac4f122398b9faf14ca610a89e1ea123ac4028346479f1f9742917a