cis-gcp-cos-6-2-11

name	cis-gcp-cos-6.2.11
description	Ensure no users have .forward files
category	cis-gcp-cos
version	1.2.0
author	cyberstrike-official
tags	["cis","gcp","container-optimized-os","user-accounts","forward-files"]
cis_id	6.2.11
cis_benchmark	CIS Google Container-Optimized OS Benchmark v1.2.0
tech_stack	["gcp","linux"]
cwe_ids	[]
chains_with	[]
prerequisites	[]
severity_boost	{}

6.2.11 Ensure no users have .forward files (Automated)

Description

The .forward file specifies an email address to forward the user's mail to.

Rationale

Use of the .forward file poses a security risk in that sensitive data may be inadvertently transferred outside the organization. The .forward file also poses a risk as it can be used to execute commands that may perform unintended actions.

Audit Procedure

Run the following script and verify no results are returned:

#!/bin/bash

grep -E -v '^(root|halt|sync|shutdown)' /etc/passwd | awk -F: '($7 != "'"$(which nologin)"'" && $7 != "/bin/false") { print $1 " " $6 }' | while read user dir; do
  if [ ! -d "$dir" ]; then
    echo "The home directory ($dir) of user $user does not exist."
  else
    if [ ! -h "$dir/.forward" -a -f "$dir/.forward" ]; then
      echo ".forward file $dir/.forward exists"
    fi
  fi
done

Expected Result

No results should be returned.

Remediation

Making global modifications to users' files without alerting the user community can result in unexpected outages and unhappy users. Therefore, it is recommended that a monitoring policy be established to report user .forward files and determine the action to be taken in accordance with site policy.

Additional Information

On some distributions the /sbin/nologin should be replaced with .