Minimize the admission of containers with added capabilities.
Set up the kubernetes integration.
Description
Do not generally permit containers with capabilities assigned beyond the default set.
Rationale
Containers run with a default set of capabilities as assigned by the Container Runtime. Capabilities outside this set can be added to containers which could expose them to risks of container breakout attacks. There should be at least one PodSecurityPolicy (PSP) defined which prevents containers with capabilities beyond the default set from launching. If you need to run containers with additional capabilities, this should be defined in a separate PSP and you should carefully check RBAC controls to ensure that only limited service accounts and users are given permission to access that PSP.
Audit
Get the set of PSPs with the following command: kubectl get psp
Verify that there are no PSPs present which have allowedCapabilities set to anything other than an empty array.
Ensure that allowedCapabilities is not present in PSPs for the cluster unless it is set to an empty array.
Impact
Pods with containers which require capabilities without the default set will not be permitted.
Default value
By default, PodSecurityPolicies are not defined.
References
- https://kubernetes.io/docs/concepts/policy/pod-security-policy/#enabling-pod-security-policies
- https://www.nccgroup.trust/uk/our-research/abusing-privileged-and-unprivileged-linux-containers/
CIS controls
Version 6.5.1 Minimize And Sparingly Use Administrative Privileges - Minimize administrative privileges and only use administrative accounts when they are required. Implement focused auditing on the use of administrative privileged functions and monitor for anomalous behavior.
