# Cis Ubuntu1804 V220 6 1 6

> Ensure permissions on /etc/shadow- are configured

- Skill: `cyberstrikeus/cis-ubuntu1804-v220-6-1-6` (Agent Skill)
- Install (CLI): `npx skillmds@latest add cyberstrikeus/cis-ubuntu1804-v220-6-1-6`
- Raw SKILL.md: https://api.skillmd.com/api/skills/cyberstrikeus/cis-ubuntu1804-v220-6-1-6/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-ubuntu1804-v220-6-1-6

---


# 6.1.6 Ensure permissions on /etc/shadow- are configured (Automated)

## Profile

- Level 1 - Server
- Level 1 - Workstation

## Description

The `/etc/shadow-` file is used to store backup information about user accounts that is critical to the security of those accounts, such as the hashed password and other security information.

## Rationale

It is critical to ensure that the `/etc/shadow-` file is protected from unauthorized access. Although it is protected by default, the file permissions could be changed either inadvertently or through malicious actions.

## Audit Procedure

### Command Line

Run the following command to verify `/etc/shadow-` is mode 640 or more restrictive, `Uid` is `0/root` and `Gid` is `0/root` or `{GID}/shadow`:

```bash
# stat -Lc 'Access: (%#a/%A) Uid: ( %u/ %U) Gid: ( %g/ %G)' /etc/shadow-
```

## Expected Result

```
Access: (0640/-rw-r-----) Uid: ( 0/ root) Gid: ( 42/ shadow)
```

## Remediation

### Command Line

Run one of the following commands to set ownership of `/etc/shadow-` to `root` and group to either `root` or `shadow`:

```bash
# chown root:shadow /etc/shadow-
  -OR-
# chown root:root /etc/shadow-
```

Run the following command to remove excess permissions from `/etc/shadow-`:

```bash
# chmod u-x,g-wx,o-rwx /etc/shadow-
```

## Default Value

Access: (0640/-rw-r-----) Uid: ( 0/ root) Gid: ( 42/ shadow)

## References

1. NIST SP 800-53 Rev. 5: AC-3. MP-2

## CIS Controls

- v8: **3.3** Configure Data Access Control Lists
- v7: **14.6** Protect Information through Access Control Lists