cis-ubuntu1804-v220-5-2-3-11

name	cis-ubuntu1804-v220-5-2-3-11
version	2.2.0
date_published	"2024-01-01T00:00:00.000Z"
category	cis-logging
description	Ensure successful file system mounts are collected
author	CIS Benchmarks
tags	["cis","ubuntu","linux","ubuntu-18.04","auditing","auditd"]
target	{"platform":"linux","version":"18.04"}
severity_boost	{}

5.2.3.11 Ensure successful file system mounts are collected

Profile Applicability

• Level 2 - Server
• Level 2 - Workstation

Description

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.

Rationale

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.

Audit

Run the following command to verify auditd is configured in accordance with site policy.

On disk configuration

64 Bit systems

UID_MIN=$(awk '/^\s*UID_MIN/{print $2}' /etc/login.defs)
[ -n "${UID_MIN}" ] && awk "/^ *-a *always,exit/ \
&&(/ -F *arch=b(32|64)/) \
&&/ -S/ \
&&/mount/ \
&&(/ key= *[!-~]* *$/||/ -k *[!-~]* *$/)/" /etc/audit/rules.d/*.rules \
|| printf "ERROR: Variable 'UID_MIN' is unset.\n"

Verify output includes:

-a always,exit -F arch=b64 -S mount -F auid>=1000 -F auid!=unset -k mounts
-a always,exit -F arch=b32 -S mount -F auid>=1000 -F auid!=unset -k mounts

Running configuration

64 Bit systems

UID_MIN=$(awk '/^\s*UID_MIN/{print $2}' /etc/login.defs)
[ -n "${UID_MIN}" ] && auditctl -l | awk  \
||