Information
Do not generally permit containers to be run as the root user.
Rationale:
Containers may run as any Linux user. Containers which run as the root user, whilst constrained by Container Runtime security features still have a escalated likelihood of container breakout.
Ideally, all containers should run as a defined non-UID 0 user.
There should be at least one admission control policy defined which does not permit root containers.
If you need to run root containers, this should be defined in a separate policy and you should carefully check to ensure that only limited service accounts and users are given permission to use that policy.
Impact:
Pods with containers which run as the root user will not be permitted.
NOTE: Nessus has not performed this check. Please review the benchmark to ensure target compliance.
Solution
Create a policy for each namespace in the cluster, ensuring that either MustRunAsNonRoot or MustRunAs with the range of UIDs not including 0, is set.
Default Value:
By default, there are no restrictions on the use of root containers and if a User is not specified in the image, the container will run as root.