Disable legacy client certificate authentication for the GKE API server

How it is checked

Audit method: Shell command

v=$(gcloud container clusters describe "${GKE_CLUSTER:?set GKE_CLUSTER}" --location "${GKE_LOCATION:?set GKE_LOCATION}" ${GKE_PROJECT:+--project=$GKE_PROJECT} --format='value(masterAuth.clientCertificate)') || exit 1
if [ -z "$v" ]; then echo compliant; else echo "noncompliant: masterAuth.clientCertificate=$v"; fi

Expected output

compliant

How it is fixed

Fix method: Guidance or infrastructure patch

For new clusters, create the cluster without issuing a legacy client certificate by using the --no-issue-client-certificate flag. gcloud container clusters create $CLUSTER_NAME \ --location $LOCATION \ --project $PROJECT_ID \ --no-issue-client-certificate For existing clusters where a legacy client certificate was already issued, GKE does not provide a direct method to remove that client certificate from the cluster. To fully remediate the setting, create a replacement cluster with --no-issue-client-certificate, migrate workloads, validate access, and decommission the old cluster after migration. Note: If immediate replacement is not practical, reduce risk on the existing cluster by ensuring RBAC is enabled and that the legacy client certificate has no Kubernetes RBAC permissions.

Check this host

Run this on a machine you are allowed to audit. The scan is read-only.

tmaegis scan --target gke