Cis K8S V1120 5.2.5

5.2.5 Minimize the admission of containers wishing to share the host network namespace (Manual)

Profile Applicability

• Level 1 - Master Node

Description

Do not generally permit containers to be run with the hostNetwork flag set to true.

Rationale

A container running in the host's network namespace could access the local loopback device, and could access network traffic to and from other pods.

There should be at least one admission control policy defined which does not permit containers to share the host network namespace.

If you need to run containers which require access to the host's network namespaces, 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 defined with spec.hostNetwork: true will not be permitted unless they are run under a specific policy.

Audit Procedure

To fetch hostNetwork from each pod:

kubectl get pods -A -o=jsonpath=$'{range .items[*]}{@.metadata.name}: {@.spec.hostNetwork}\n{end}'

Remediation

Add policies to each namespace in the cluster which has user workloads to restrict the admission of hostNetwork containers.

Default Value

By default, there are no restrictions on the creation of hostNetwork containers.

References

1. https://kubernetes.io/docs/concepts/security/pod-security-standards/

CIS Controls