cis-ubuntu1804-v220-6-2-6

name	cis-ubuntu1804-v220-6-2-6
description	Ensure no duplicate GIDs exist
category	cis-iam
version	2.2.0
author	cyberstrike-official
tags	["cis","ubuntu","linux","ubuntu-18.04","groups"]
cis_id	6.2.6
cis_benchmark	CIS Ubuntu Linux 18.04 LTS Benchmark v2.2.0
tech_stack	["ubuntu","linux"]
cwe_ids	[]
chains_with	[]
prerequisites	[]
severity_boost	{}

6.2.6 Ensure no duplicate GIDs exist (Automated)

Profile

• Level 1 - Server
• Level 1 - Workstation

Description

Although the groupadd program will not let you create a duplicate Group ID (GID), it is possible for an administrator to manually edit the /etc/group file and change the GID field.

Rationale

User groups must be assigned unique GIDs for accountability and to ensure appropriate access protections.

Audit Procedure

Command Line

Run the following script and verify no results are returned:

#!/usr/bin/env bash

{
  while read -r l_count l_gid; do
      if [ "$l_count" -gt 1 ]; then
        echo -e "Duplicate GID: \"$l_gid\" Groups: \"$(awk -F: '($3 == n) { print $1 }' n=$l_gid /etc/group | xargs)\""
      fi
  done < <(cut -f3 -d":" /etc/group | sort -n | uniq -c)
}

Expected Result

No output should be returned.

Remediation

Command Line

Based on the results of the audit script, establish unique GIDs and review all files owned by the shared GID to determine which group they are supposed to belong to.

References

1. NIST SP 800-53 Rev. 5: CM-1, CM-2, CM-6, CM-7, IA-5

Additional Information

You can also use the grpck command to check for other inconsistencies in the /etc/group file.

CIS Controls

• v8: 5.2 Use Unique Passwords
• v7: 4.4 Use Unique Passwords