Backstage Kubernetes Plugin CVE-2026-106563

Attacker must be an authenticated Backstage user who already holds Kubernetes read permissions (PR:L), and must target the specific DEPRECATED kubernetes services endpoint (POST /api/kubernetes/services/:serviceId in @backstage/plugin-kubernetes-backend) by supplying crafted entity data in the request body that the vulnerable code passes through without resolving it against the catalog. Limiting factors: exploitation is impossible for unauthenticated users or users lacking Kubernetes read permission; it only affects the deprecated services endpoint (not current endpoints); the result is read-only Kubernetes object metadata with no integrity or availability impact; and the high attack complexity (AC:H) reflects the need to craft an entity reference that evades validation. Not exploitable against instances already on @backstage/plugin-kubernetes-backend 0.21.8 or later.

This is a moderate, authorization-boundary (CWE-20) issue rather than a high-urgency priority. The provided CVSS 3.1 vector (AV:N/AC:H/PR:L/UI:N/S:U/C:H/I:N/A:N = 5.3) indicates network reachability but requires existing low privileges (PR:L) AND high attack complexity (AC:H), which materially constrains real-world exploitation. Exploitation status is 'no public exploit identified at time of analysis' - no POC, no EPSS score, and no CISA KEV listing were provided, so there is no evidence of active or at-scale exploitation; this looks like a privilege-scoping/IDOR-style defect most relevant to multi-tenant Backstage deployments. One signal to flag: the vendor rated C:H, but the description explicitly limits exposure to 'read-only access to Kubernetes object metadata' - no integrity or availability impact and no write/code execution - so the C:H rating is arguably generous for metadata-only disclosure; verify sensitivity of exposed metadata against your environment. Net: real but low-to-moderate priority, driven by the need for a pre-authenticated user who already holds Kubernetes read permissions.

An authenticated Backstage user who already holds Kubernetes read permissions issues a request to the deprecated kubernetes services endpoint with crafted entity data that is not properly resolved against the catalog, causing the backend to return Kubernetes workload metadata for clusters/entities outside the user's intended authorization scope. No public exploit code was identified, and the high attack complexity (AC:H) means the attacker must shape the entity reference payload precisely to bypass validation.