Cis Docker 5.26

5.26 Ensure that the container is restricted from acquiring additional privileges (Manual)

Profile Applicability

• Level 1 - Docker - Linux

Description

You should restrict the container from acquiring additional privileges via suid or sgid bits.

Rationale

A process can set the no_new_priv bit in the kernel and this persists across forks, clones and execve. The no_new_priv bit ensures that the process and its child processes do not gain any additional privileges via suid or sgid bits. This reduces the danger associated with many operations because the possibility of subverting privileged binaries is lessened.

Impact

The no_new_priv option prevents LSMs like SELinux from allowing processes to acquire new privileges

Audit Procedure

You should run the following command:

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

This command should return all the security options currently configured for containers. no-new-privileges should be one of them.

Note that the SecurityOpt response will be empty (i.e. SecurityOpt=<no value>) even if "no-new-privileges": true has been configured in the Docker daemon.json configuration file.

Remediation

You should start your container with the options below:

docker run --rm -it --security-opt=no-new-privileges ubuntu bash

Default Value

By default, new privileges are not restricted.

References

1. https://docs.docker.com/engine/reference/run/#security-configuration
2. https://www.kernel.org/doc/Documentation/prctl/no_new_privs.txt

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