# Cis Ubuntu1204 V110 13 17

> Check for Duplicate User Names

- Skill: `cyberstrikeus/cis-ubuntu1204-v110-13-17` (Agent Skill)
- Install (CLI): `npx skillmds@latest add cyberstrikeus/cis-ubuntu1204-v110-13-17`
- Raw SKILL.md: https://api.skillmd.com/api/skills/cyberstrikeus/cis-ubuntu1204-v110-13-17/raw
- Safety review: PASS (external: skill-scanner PASS, skillspector CAUTION)
- Works with: Claude Code, Claude.ai, OpenAI Codex
- Category: Coding & Dev Tools
- Author: cyberstrikeus (https://skillmd.com/u/cyberstrikeus)
- Updated: 2026-09-17
- Page: https://skillmd.com/skills/cyberstrikeus/cis-ubuntu1204-v110-13-17

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# 13.17 Check for Duplicate User Names (Scored)

## Profile Applicability

- Level 1

## 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.

## Audit Procedure

### Using Command Line

This script checks to make sure all user names in the `/etc/passwd` file are unique.

```bash
#!/bin/bash
cat /etc/passwd | /usr/bin/cut -f1 -d":" | /usr/bin/sort -n | /usr/bin/uniq -c |\
while read x ; do
    [ -z "${x}" ] && break
    set - $x
    if [ $1 -gt 1 ]; then
        uids=`/usr/bin/awk -F: '($1 == n) { print $3 }' n=$2 \
            /etc/passwd | xargs`
        echo "Duplicate User Name ($2): ${uids}"
    fi
done
```

## Expected Result

No output should be returned. Any output indicates duplicate user names exist in `/etc/passwd`.

## Remediation

### Using Command Line

Based on the results of the 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

The `useradd` command prevents creation of duplicate user names by default.

## References

- CIS Ubuntu 12.04 LTS Server Benchmark v1.1.0

## Profile

Level 1 - Scored