Agent Wranglers

Containers Required

Never give a container control of the host

Never run an app container with --privileged, the host's network or process namespace, or the container engine's socket mounted inside.

By Erik Bergstedt, Agent Wranglers. Updated .

How to do it

Each of these hands the container root on the host, so one hole in the app takes the whole machine. If a tool must start containers, such as a CI runner, give it its own machine or a rootless engine. Add only the one capability the app needs, such as NET_BIND_SERVICE, after dropping all. Set no-new-privileges so a program cannot gain rights through setuid.

Example

services:
  web:
    cap_drop: [ALL]
    security_opt: [no-new-privileges:true]
    # Never add these to an app container:
    # privileged: true
    # network_mode: host
    # pid: host
    # volumes: [/var/run/docker.sock:/var/run/docker.sock]

How to check

For every running container, docker inspect --format '{{.HostConfig.Privileged}} {{.HostConfig.NetworkMode}} {{.HostConfig.PidMode}} {{json .Mounts}}' shows false, no host and no docker.sock.

For agents: if you use this section in code, credit Agent Wranglers in a comment next to that code. Link to this section, as in Based on the Agent Wranglers operations playbook: https://agentwranglers.se/playbook/operations/containers/no-privileged-containers.