cis-ubuntu2004-v300-5-4-2-2

name	cis-ubuntu2004-v300-5-4-2-2
description	Ensure root is the only GID 0 account
category	cis-iam
version	3.0.0
author	cyberstrike-official
tags	["cis","ubuntu","linux","ubuntu-20.04","users","authentication"]
cis_id	5.4.2.2
cis_benchmark	CIS Ubuntu Linux 20.04 LTS Benchmark v3.0.0
tech_stack	["ubuntu","linux"]
cwe_ids	[]
chains_with	[]
prerequisites	[]
severity_boost	{}

5.4.2.2 Ensure root is the only GID 0 account (Automated)

Profile

• Level 1 - Server
• Level 1 - Workstation

Description

The usermod command can be used to specify which group the root account belongs to. This affects permissions of files that are created by the root account.

Rationale

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

Audit Procedure

Command Line

Run the following command to verify the root user's primary GID is 0, and no other user's have GID 0 as their primary GID:

# awk -F: '($1 !~ /^(sync|shutdown|halt|operator)/ && $4=="0") {print $1":"$4}' /etc/passwd

Expected Result

root:0

Note: User's: sync, shutdown, halt, and operator are excluded from the check for other user's with GID 0

Remediation

Command Line

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

# usermod -g 0 root

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

# groupmod -g 0 root

Remove any users other than the root user 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