# Cis Ubuntu1804 V220 1 8 10

> Ensure XDCMP is not enabled

- Skill: `cyberstrikeus/cis-ubuntu1804-v220-1-8-10` (Agent Skill)
- Install (CLI): `npx skillmds@latest add cyberstrikeus/cis-ubuntu1804-v220-1-8-10`
- Raw SKILL.md: https://api.skillmd.com/api/skills/cyberstrikeus/cis-ubuntu1804-v220-1-8-10/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-v220-1-8-10

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# 1.8.10 Ensure XDCMP is not enabled (Automated)

## Profile Applicability

- Level 1 - Server
- Level 1 - Workstation

## Description

X Display Manager Control Protocol (XDMCP) is designed to provide authenticated access to display management services for remote displays.

## Rationale

XDMCP is inherently insecure.

- XDMCP is not a ciphered protocol. This may allow an attacker to capture keystrokes entered by a user.
- XDMCP is vulnerable to man-in-the-middle attacks. This may allow an attacker to steal the credentials of legitimate users by impersonating the XDMCP server.

## Audit Procedure

### Command Line

Run the following command and verify the output:

```bash
grep -Eis '^\s*Enable\s*=\s*true' /etc/gdm3/custom.conf
```

## Expected Result

Nothing should be returned.

## Remediation

### Command Line

Edit the file `/etc/gdm3/custom.conf` and remove the line:

```
Enable=true
```

## Default Value

false (This is denoted by no Enabled= entry in the file `/etc/gdm3/custom.conf` in the [xdmcp] section)

## References

1. NIST SP 800-53 Rev. 5: SI-4