Containers should not share the host's user namespaces
Set up the docker integration.
Description
You should not share the host’s user namespaces with containers running on it.
Rationale
User namespaces ensure that a root process inside the container will be mapped to a non-root process outside the container. Sharing the user namespaces of the host with the container does not therefore isolate users on the host from users in the containers.
Audit
Run this command and ensure that it does not return any value for UsernsMode. If it returns a value of host, it means that the host user namespace is shared with its containers: docker ps --quiet --all | xargs docker inspect --format '{{ .Id }}: UsernsMode={{ .HostConfig.UsernsMode }}'
Do not share user namespaces between host and containers. For example, do not run the command docker run --rm -it --userns=host ubuntu bash
Impact
None
Default value
By default, the host user namespace is shared with containers unless user namespace support is enabled.
References
- https://docs.docker.com/engine/security/userns-remap/
- https://docs.docker.com/engine/reference/commandline/run/#options
- https://github.com/docker/docker/pull/12648
- https://events.linuxfoundation.org/sites/events/files/slides/User%20Namespaces%20-%20ContainerCon%202015%20-%2016-9-final_0.pdf
CIS controls
Version 6
12 Boundary Defense Boundary Defense
