C-0281 - Minimize access to webhook configuration objects

Framework

cis-v1.10.0

Severity

Medium

Description of the the issue

Users with rights to create/modify/delete validatingwebhookconfigurations or mutatingwebhookconfigurations can control webhooks that can read any object admitted to the cluster, and in the case of mutating webhooks, also mutate admitted objects. This could allow for privilege escalation or disruption of the operation of the cluster.

Related resources

ClusterRole, ClusterRoleBinding, Role, RoleBinding

What does this control test

Check which subjects have RBAC permissions to create/modify/delete validatingwebhookconfigurations or mutatingwebhookconfigurations objects.

How to check it manually

Review the users who have access to validatingwebhookconfigurations or mutatingwebhookconfigurations objects in the Kubernetes API.

Remediation

Where possible, remove access to the validatingwebhookconfigurations or mutatingwebhookconfigurations objects

Impact Statement

Default Value

By default in a kubeadm cluster the following list of principals have create/modify/delete privileges on validatingwebhookconfigurations/mutatingwebhookconfigurations objects CLUSTERROLEBINDING SUBJECT TYPE SA-NAMESPACEcluster-admin system:masters Group system:controller:clusterrole-aggregation-controller clusterrole-aggregation-controller ServiceAccount kube-systemsystem:controller:daemon-set-controller daemon-set-controller ServiceAccount kube-systemsystem:controller:job-controller job-controller ServiceAccount kube-systemsystem:controller:persistent-volume-binder persistent-volume-binder ServiceAccount kube-systemsystem:controller:replicaset-controller replicaset-controller ServiceAccount kube-systemsystem:controller:replication-controller replication-controller ServiceAccount kube-systemsystem:controller:statefulset-controller statefulset-controller ServiceAccount kube-system

Example

No example