Ensure that the host's user namespaces are not shared

MediumLevel 1Automateddocker

Description

UsernsMode=host disables user namespace remapping for the container, so root in the container is root on the host. The audit inspects every running container (docker ps -q) and prints the offending names; a host with no running containers is compliant.

How it is checked

Audit method: Shell command

shell

ids=$(docker ps -q) || exit 1; [ -z "$ids" ] && { echo compliant; exit 0; }; out=$(docker inspect --format '{{.Name}} {{.HostConfig.UsernsMode}}' $ids) || exit 1; bad=$(printf '%s\n' "$out" | awk '$2=="host"{print $1}'); [ -z "$bad" ] && echo compliant || printf '%s\n' "$bad"

Expected output: compliant

How it is fixed

Fix method: Guidance or infrastructure patch

Redeploy without --userns=host (compose: remove 'userns_mode: host').

Properties

Operating systems: Any
Tags: dockerruntime
Reference: CIS Docker Benchmark v1.9.0 - 5.31 Ensure that the host's user namespaces are not shared

Check this host

Run this on a machine you are allowed to audit. The scan is read-only.

shell

tmaegis scan --target docker