The API server defaults to allow anonymous auth, meaning that incoming requests that are not authenticated will be implicitly given a username
system:anonymous and be part of the
system:unauthenticated group. While this user may not have permission to anything, problems related to allowing anonymous authentication are still possible, such as vulnerabilities like the "Billion Laughs" attack.
Disabling anonymous authentication only requires passing an argument to the API server:
apiVersion: crit.sh/v1alpha2 kind: ControlPlaneConfiguration kubeAPIServer: extraArgs: anonymous-auth: false
Liveness probes will fail for static pods should anonymous-auth be set to false. Crit addresses this by detecting when
--anonymous-auth has been disabled and adds a special healthcheck-proxy sidecar to the apiserver static pod. It acts as a reverse proxy with the frontend effectively accepting anonymous traffic and the backend using an authenticated user. The backend connection is established with the built-in
system:basic-info-viewer user to limit the auth to only being able to look at health and version information.