# Cis Ubuntu1804 V220 4 5 1 6

> Ensure the number of changed characters in a new password is configured

- Skill: `cyberstrikeus/cis-ubuntu1804-v220-4-5-1-6` (Agent Skill)
- Install (CLI): `npx skillmds@latest add cyberstrikeus/cis-ubuntu1804-v220-4-5-1-6`
- Raw SKILL.md: https://api.skillmd.com/api/skills/cyberstrikeus/cis-ubuntu1804-v220-4-5-1-6/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-ubuntu1804-v220-4-5-1-6

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# CIS Ubuntu Linux 18.04 LTS Benchmark v2.2.0 - Control 4.5.1.6

## Profile Applicability

- Level 1 - Server
- Level 1 - Workstation

## Description

The `pwquality` `difok` option sets the number of characters in a password that must not be present in the old password.

## Rationale

Use of a complex password helps to increase the time and resources required to compromise the password. Password complexity, or strength, is a measure of the effectiveness of a password in resisting attempts at guessing and brute-force attacks.

Password complexity is one factor of several that determines how long it takes to crack a password. The more complex the password, the greater the number of possible combinations that need to be tested before the password is compromised.

## Audit Procedure

### Command Line

Run the following command to verify that the `difok` option in `/etc/security/pwquality.conf` is set to `2` or more:

```bash
grep -Pi '^\h*difok\h*=\h*([2-9]|[1-9][0-9]+)\b' /etc/security/pwquality.conf
```

### Expected Result

```
difok = 2
```

Or higher.

## Remediation

### Command Line

Edit or add the following line in `/etc/security/pwquality.conf` to a value of `2` or more:

```
difok = 2
```

## Default Value

difok = 1

## References

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

## CIS Controls

v8 - 5.2 Use Unique Passwords - Use unique passwords for all enterprise assets.

v7 - 4.4 Use Unique Passwords.

## Profile Applicability

- Level 1 - Server
- Level 1 - Workstation

## Assessment Status

Automated