# Cis Ubuntu2004 V300 5 4 2 3

> Ensure group root is the only GID 0 group

- Skill: `cyberstrikeus/cis-ubuntu2004-v300-5-4-2-3` (Agent Skill)
- Install (CLI): `npx skillmds@latest add cyberstrikeus/cis-ubuntu2004-v300-5-4-2-3`
- Raw SKILL.md: https://api.skillmd.com/api/skills/cyberstrikeus/cis-ubuntu2004-v300-5-4-2-3/raw
- Safety review: PASS (external: skill-scanner PASS, skillspector PASS)
- 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-ubuntu2004-v300-5-4-2-3

---


# 5.4.2.3 Ensure group root is the only GID 0 group (Automated)

## Profile

- Level 1 - Server
- Level 1 - Workstation

## Description

The `groupmod` command can be used to specify which group the `root` group belongs to. This affects permissions of files that are group owned by the `root` group.

## Rationale

Using GID 0 for the `root` group helps prevent `root` group owned files from accidentally becoming accessible to non-privileged users.

## Audit Procedure

### Command Line

Run the following command to verify no group other than `root` is assigned GID 0:

```bash
# awk -F: '$3=="0"{print $1":"$3}' /etc/group
```

## Expected Result

```
root:0
```

## Remediation

### Command Line

Run the following command to set the `root` group's GID to 0:

```bash
# groupmod -g 0 root
```

Remove any groups other than the `root` group with GID 0 or assign them a new GID if appropriate.

## Default Value

None specified.

## References

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

## CIS Controls

v8 - 3.3 Configure Data Access Control Lists: Configure data access control lists based on a user's need to know. Apply data access control lists, also known as access permissions, to local and remote file systems, databases, and applications. (IG 1, IG 2, IG 3)

v7 - 14.6 Protect Information through Access Control Lists: Protect all information stored on systems with file system, network share, claims, application, or database specific access control lists. These controls will enforce the principle that only authorized individuals should have access to the information based on their need to access the information as a part of their responsibilities. (IG 1, IG 2, IG 3)

MITRE ATT&CK Mappings: T1548, T1548.000 - Tactics: TA0005 - Mitigations: M1026