cis-ubuntu2004-v300-7-2-7

name	cis-ubuntu2004-v300-7-2-7
description	Ensure no duplicate user names exist
category	cis-iam
version	3.0.0
author	cyberstrike-official
tags	["cis","ubuntu","linux","ubuntu-20.04","users"]
cis_id	7.2.7
cis_benchmark	CIS Ubuntu Linux 20.04 LTS Benchmark v3.0.0
tech_stack	["ubuntu","linux"]
cwe_ids	[]
chains_with	[]
prerequisites	[]
severity_boost	{}

7.2.7 Ensure no duplicate user names exist (Automated)

Profile

• Level 1 - Server
• Level 1 - Workstation

Description

Although the useradd program will not let you create a duplicate user name, it is possible for an administrator to manually edit the /etc/passwd file and change the user name.

Rationale

If a user is assigned a duplicate user name, it will create and have access to files with the first UID for that username in /etc/passwd. For example, if "test4" has a UID of 1000 and a subsequent "test4" entry has a UID of 2000, logging in as "test4" will use UID 1000. Effectively, the UID is shared, which is a security problem.

Impact

None

Audit Procedure

Command Line

Run the following script and verify no results are returned:

#!/usr/bin/env bash

{
    while read -r l_count l_user; do
        if [ "$l_count" -gt 1 ]; then
            echo -e "Duplicate User: \"$l_user\" Users: \"$(awk -F: '($1 == n) { print $1 }' n=$l_user /etc/passwd | xargs)\""
        fi
    done < <(cut -f1 -d":" /etc/passwd | sort -n | uniq -c)
}

Expected Result

No output should be returned.

Remediation

Command Line

Based on the results of the audit script, establish unique user names for the users. File ownerships will automatically reflect the change as long as the users have unique UIDs.

Default Value

N/A

References

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

CIS Controls

Controls Version	Control	IG 1	IG 2