# Cis Docker 5.30

> Ensure that Docker's default bridge docker0 is not used

- Skill: `cyberstrikeus/cis-docker-5-30` (Agent Skill)
- Install (CLI): `npx skillmds@latest add cyberstrikeus/cis-docker-5-30`
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- Works with: Claude Code, Claude.ai, OpenAI Codex
- Category: DevOps & Infra
- Author: cyberstrikeus (https://skillmd.com/u/cyberstrikeus)
- Updated: 2026-09-17
- Page: https://skillmd.com/skills/cyberstrikeus/cis-docker-5-30

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# 5.30 Ensure that Docker's default bridge "docker0" is not used (Manual)

## Profile Applicability

- Level 2 - Docker - Linux

## Description

You should not use Docker's default bridge `docker0`. Instead you should use Docker's user-defined networks for container networking.

## Rationale

Docker connects virtual interfaces created in bridge mode to a common bridge called `docker0`. This default networking model is vulnerable to ARP spoofing and MAC flooding attacks as there is no filtering applied to it.

## Impact

User-defined networks need to be configured and managed in line with organizational security policy.

## Audit Procedure

You should run the command below, and verify that containers are on a user-defined network and not the default `docker0` bridge.

```
docker network ls --quiet | xargs docker network inspect --format '{{ .Name }}: {{ .Options }}'
```

## Remediation

You should follow the Docker documentation and set up a user-defined network. All the containers should be run in this network.

## Default Value

By default, Docker runs containers within the default `docker0` bridge.

## References

1. https://docs.docker.com/network/bridge/

## CIS Controls

| Controls Version | Control                                                                                                                                                                                                                                              | IG 1 | IG 2 | IG 3 |
| ---------------- | ---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | ---- | ---- | ---- |
| v8               | 4.8 Uninstall or Disable Unnecessary Services on Enterprise Assets and Software<br>Uninstall or disable unnecessary services on enterprise assets and software, such as an unused file sharing service, web application module, or service function. |      | ●    | ●    |
| v6               | 9 Limitation and Control of Network Ports, Protocols, and Services<br>Limitation and Control of Network Ports, Protocols, and Services                                                                                                               |      |      |      |