Ensure that Linux kernel capabilities are restricted within containers

MediumLevel 1Automateddocker

Description

Containers should run with the minimum Linux capabilities; the benchmark specifically asks for NET_RAW to be dropped unless required. Flags containers whose CapDrop contains neither ALL nor NET_RAW (review CapAdd separately). 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}} {{range .HostConfig.CapDrop}}{{.}},{{end}}' $ids) || exit 1; bad=$(printf '%s\n' "$out" | awk 'toupper($0) !~ /(^| |,)(CAP_)?(ALL|NET_RAW),/ {print $1}'); [ -z "$bad" ] && echo compliant || printf '%s\n' "$bad"

Expected output: compliant

How it is fixed

Fix method: Guidance or infrastructure patch

Run containers with --cap-drop=ALL (or at least --cap-drop=NET_RAW) and add back only required capabilities with --cap-add.

Properties

Operating systems: Any
Tags: dockerruntime
Reference: CIS Docker Benchmark v1.9.0 - 5.4 Ensure that Linux kernel capabilities are restricted within containers

Check this host

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

shell

tmaegis scan --target docker