Cis Ubuntu2004 V300 7 2 4

---
name: cis-ubuntu2004-v300-7-2-4
description: "Ensure shadow group is empty"
category: cis-iam
version: "3.0.0"
author: cyberstrike-official
tags: [cis, ubuntu, linux, ubuntu-20.04, groups]
cis_id: "7.2.4"
cis_benchmark: "CIS Ubuntu Linux 20.04 LTS Benchmark v3.0.0"
tech_stack: [ubuntu, linux]
cwe_ids: []
chains_with: []
prerequisites: []
severity_boost: {}
---

# 7.2.4 Ensure shadow group is empty (Automated)

## Profile

- Level 1 - Server
- Level 1 - Workstation

## Description

The shadow group allows system programs which require access the ability to read the /etc/shadow file. No users should be assigned to the shadow group.

## Rationale

Any users assigned to the shadow group would be granted read access to the /etc/shadow file. If attackers can gain read access to the `/etc/shadow` file, they can easily run a password cracking program against the hashed passwords to break them. Other security information that is stored in the `/etc/shadow` file (such as expiration) could also be useful to subvert additional user accounts.

## Impact

None

## Audit Procedure

### Command Line

Run the following commands and verify no results are returned:

```bash
# awk -F: '($1=="shadow") {print $NF}' /etc/group
# awk -F: '($4 == '"$(getent group shadow | awk -F: '{print $3}' | xargs)"') {print " - user: \"" $1 "\" primary group is the shadow group"}' /etc/passwd
```

## Expected Result

No output should be returned.

## Remediation

### Command Line

Run the following command to remove all users from the shadow group:

```bash
# sed -ri 's/(^shadow:[^:]*:[^:]*:[^:]*:)([^:]+$)/\1/' /etc/group
```

Change the primary group of any users with shadow as their primary group.

```bash
# usermod -g <primary group> <user>
```

## Default Value

N/A

## References

1. NIST SP 800-53 Rev. 5: IA-5

## CIS Controls

| Controls Version | Control                                               | IG 1 | IG 2 | IG 3 |
| ---------------- | ----------------------------------------------------- | ---- | ---- | ---- |
| v8               | 3.3 Configure Data Access Control Lists               | X    | X    | X    |
| v7               | 14.6 Protect Information through Access Control Lists | X    | X    | X    |

MITRE ATT&CK Mappings:

| Techniques / Sub-techniques | Tactics | Mitigations |
| --------------------------- | ------- | ----------- |
| T1003, T1003.008            | TA0005  | M1022       |