# Cis Ubuntu2004 V300 1 7 10

> Ensure XDMCP is not enabled

- Skill: `cyberstrikeus/cis-ubuntu2004-v300-1-7-10` (Agent Skill)
- Install (CLI): `npx skillmds@latest add cyberstrikeus/cis-ubuntu2004-v300-1-7-10`
- Raw SKILL.md: https://api.skillmd.com/api/skills/cyberstrikeus/cis-ubuntu2004-v300-1-7-10/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-ubuntu2004-v300-1-7-10

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# 1.7.10 Ensure XDMCP is not enabled (Automated)

## Profile

- 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 script and verify the output:

```bash
#!/usr/bin/env bash

{
   while IFS= read -r l_file; do
      awk '/\[xdmcp\]/{ f = 1;next } /\[/{ f = 0 } f {if (/^\s*Enable\s*=\s*true/) print "The file: \""$l_file"\" includes: \"" $0 "\" in the \"[xdmcp]\" block"}' "$l_file"
   done < <(grep -Psil -- '^\h*\[xdmcp\]' /etc/{gdm3,gdm}/{custom,daemon}.conf)
}
```

Nothing should be returned.

## Expected Result

No output should be returned, confirming XDMCP is not enabled.

## Remediation

### Command Line

Edit the `/etc/gdm3/custom.conf` or `/etc/gdm/custom.conf` file and remove the `Enable=true` option from the `[xdmcp]` section if it exists.

## References

1. NIST SP 800-53 Rev. 5: CM-6, CM-7