CVE-2026-55636: Capsule Incomplete Fix Of CVE-2026-30963: Singular/plural Vulnerability

{
  "schema_version" : "1.4.0",
  "id" : "GHSA-gwxr-7h77-7777",
  "modified" : "2026-06-17T18:14:12Z",
  "published" : "2026-06-17T18:14:12Z",
  "aliases" : [ "CVE-2026-55636" ],
  "summary" : "Capsule: Incomplete fix of CVE-2026-30963: singular/plural typo leaves namespaces/finalize unprotected",
  "details" : "### Summary\nCapsule 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.\n\n### Details\nPUT to `/api/v1/namespaces/<ns>/finalize` has resource=namespaces (plural). The singular rule never matches. `matchPolicy: Equivalent` does not compensate.\n\n### PoC\nConfirmed 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.\n\n### Impact\nNamespace tenant-label hijack. Same threat model as CVE-2026-30963. One-char fix: `namespace/finalize` -> `namespaces/finalize`.\nThe 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.\n\n### Details\nIn 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.\n\nThe `matchPolicy: Equivalent` setting does NOT compensate (it handles API group/version variations, not resource name typos).\n\n### PoC\nConfirmed on kind cluster + Capsule v0.13.2 (Helm chart):\n```bash\n# Setup: alice with namespaces/finalize RBAC\nkubectl apply -f - <<EOF\napiVersion: rbac.authorization.k8s.io/v1\nkind: ClusterRole\nmetadata:\n  name: ns-finalize-updater\nrules:\n- apiGroups: [\"\"]\n-   resources: [\"namespaces/finalize\"]\n-   verbs: [\"update\"]\n- - apiGroups: [\"\"]\n-   resources: [\"namespaces\"]\n-   verbs: [\"get\", \"list\"]\n- EOF\n- kubectl create clusterrolebinding alice-finalize --clusterrole=ns-finalize-updater --user=alice\n# Control: normal label change DENIED\nkubectl label namespace oil-prod capsule.clastix.io/tenant=evil --overwrite --as=alice\n# Error: admission webhook denied\n\n# Bypass: finalize changes tenant label (webhook NOT invoked)\nkubectl get namespace oil-prod -o json > /tmp/ns.json\n# modify tenant label to \"hijacked\"\nkubectl replace --raw \"/api/v1/namespaces/oil-prod/finalize\" -f /tmp/ns_modified.json --as=alice\n# 200 OK - tenant label changed\n```\n\n### Impact\nNamespace tenant-label hijack via the finalize subresource bypass. Same threat model as CVE-2026-30963. One-character fix needed: `namespace/finalize` -> `namespaces/finalize`.",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:N/AC:L/PR:H/UI:R/S:U/C:L/I:H/A:L"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "Go",
      "name" : "github.com/projectcapsule/capsule"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0.13.0"
      }, {
        "fixed" : "0.13.6"
      } ]
    } ]
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/projectcapsule/capsule/security/advisories/GHSA-gwxr-7h77-7777"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/projectcapsule/capsule"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-863" ],
    "severity" : "MODERATE",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-06-17T18:14:12Z",
    "nvd_published_at" : null
  }
}