Executive brief
Capsule is a multi-tenancy framework for Kubernetes that ensures different users or teams (tenants) remain isolated within their own virtual clusters. A security flaw was identified where the system failed to monitor specific administrative sub-channels (subresources) used to update namespace metadata. If a tenant administrator is granted specific permissions by a platform manager, they could exploit this oversight to "hijack" namespaces belonging to other tenants, potentially gaining unauthorized access to resources or disrupting operations.
Technical details
Capsule uses a ValidatingWebhookConfiguration to prevent namespace hijacking by intercepting update and patch operations. However, prior to version 0.13.0, the webhook did not define interception rules for the 'namespace/finalize' and 'namespace/status' subresource APIs. These subresources can be used to modify the metadata field of a namespace, including owner references. An attacker acting as a tenant administrator with RBAC permissions to modify these subresources can patch a namespace's metadata to change its ownership to their own tenant. This bypasses Capsule's multi-tenancy isolation. The issue is fixed in version 0.13.0 by including these subresources in the webhook's interception rules.
Affected products
- Project Capsule Capsule < 0.13.0
Timeline
- 2026-05-28: patched: Version 0.13.0 released
- 2026-05-28: advisory: GitHub Security Advisory GHSA-2ww6-hf35-mfjm published
- 2026-06-01: disclosed: CVE-2026-30963 published to NVD