Capsule: Incomplete fix of CVE-2026-30963: singular/plural typo leaves namespaces/finalize unprotected
Date: 2026-06
Affected: go/github.com/projectcapsule/capsule
Attack vector: auth-bypass
Category: vulnerability-disclosure
Severity: Medium
CVE: CVE-2026-55636
CWE: CWE-863
CVSS: 5.7 (CVSS:3.1/AV:N/AC:L/PR:H/UI:R/S:U/C:L/I:H/A:L)

### 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). ###


Mitigations:

Architectural layers (MAESTRO):