Cis Docker 5.29

5.29 Ensure that the PIDs cgroup limit is used (Manual)

Profile Applicability

• Level 1 - Docker - Linux

Description

You should use the --pids-limit flag at container runtime.

Rationale

Attackers could launch a fork bomb with a single command inside the container. This fork bomb could crash the entire system and would require a restart of the host to make the system functional again. Using the PIDs cgroup parameter --pids-limit would prevent this kind of attack by restricting the number of forks that can happen inside a container within a specified time frame.

Impact

Set the PIDs limit value as appropriate. Incorrect values might leave containers unusable.

Audit Procedure

You should run the command below and ensure that PidsLimit is not set to 0 or -1. A PidsLimit of 0 or -1 means that any number of processes can be forked concurrently inside the container.

docker ps --quiet --all | xargs docker inspect --format '{{ .Id }}: PidsLimit={{ .HostConfig.PidsLimit }}'

Remediation

Use --pids-limit flag with an appropriate value when launching the container. For example:

docker run -it --pids-limit 100 <Image ID>

In the above example, the number of processes allowed to run at any given time is set to 100. After a limit of 100 concurrently running processes is reached, Docker would restrict any new process creation.

Default Value

The Default value for --pids-limit is 0 which means there is no restriction on the number of forks. Note that the PIDs cgroup limit works only for kernel versions 4.3 and higher.

References

1. https://docs.docker.com/engine/reference/commandline/run/

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