cis-ubuntu1604-v200-6-2-13

name	cis-ubuntu1604-v200-6-2-13
description	Ensure no duplicate UIDs exist
category	cis-iam
version	2.0.0
author	cyberstrike-official
tags	["cis","ubuntu","linux","ubuntu-16.04","user-management","maintenance"]
cis_id	6.2.13
cis_benchmark	CIS Ubuntu Linux 16.04 LTS Benchmark v2.0.0
tech_stack	["ubuntu","linux"]
cwe_ids	[]
chains_with	[]
prerequisites	[]
severity_boost	{}

CIS Ubuntu Linux 16.04 LTS Benchmark v2.0.0 - Control 6.2.13

Profile

• Level: 1 - Server
• Level: 1 - Workstation
• Assessment Status: Automated

Description

Although the useradd program will not let you create a duplicate User ID (UID), it is possible for an administrator to manually edit the /etc/passwd file and change the UID field.

Rationale

Users must be assigned unique UIDs for accountability and to ensure appropriate access protections.

Audit Procedure

Command Line

Run the following script and verify no results are returned:

#!/bin/bash
cut -f3 -d":" /etc/passwd | sort -n | uniq -c | while read x ; do
  [ -z "$x" ] && break
  set - $x
  if [ $1 -gt 1 ]; then
    users=$(awk -F: '($3 == n) { print $1 }' n=$2 /etc/passwd | xargs)
    echo "Duplicate UID ($2): $users"
  fi
done

Expected Result

No output should be returned.

Remediation

Command Line

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

Default Value

N/A

References

N/A

CIS Controls

Controls Version	Control	IG 1	IG 2	IG 3