Backstage Kubernetes Plugin CVE-2026-106561

Requires an authenticated Backstage user holding the standard Kubernetes resource read permission; exploitation occurs specifically through the custom resources query path of @backstage/plugin-kubernetes-backend, where Secret data and stringData values were not masked before version 0.21.9. Disclosure is strictly limited to Secrets that the Backstage service account's cluster credentials are permitted to read AND that match the targeted catalog entity's namespace and label selector; deployments whose cluster credentials grant no read access to those resources are unaffected. Limiting factors: prior authentication plus the read permission are mandatory, and the service-account RBAC scope caps what can ever be exposed.

This is a genuine but moderate-severity information-disclosure issue, not a top-priority emergency. The vendor/NVD CVSS 3.1 vector (AV:N/AC:L/PR:L/UI:N/S:C/C:L/I:N/A:N, base 5.0) indicates a network-reachable, low-complexity flaw that nevertheless requires authentication (PR:L) and yields only limited confidentiality impact with no integrity or availability effect. The scope change (S:C) is appropriate and meaningful here: the Backstage plugin leaks data belonging to a separate security authority (the connected Kubernetes cluster), and the leaked material is credentials/secrets, which raises the practical stakes above what C:L alone suggests. No EPSS score, CISA KEV listing, or public POC was provided in the input, so there is no public exploit identified at time of analysis and no evidence of active exploitation - the signals are not conflicting, they are simply absent on the exploitation-likelihood side. The realistic risk is constrained by two factors confirmed in the description: the attacker must already be an authenticated user with the standard Kubernetes resource read permission, and disclosure is bounded to secrets the Backstage service account itself can read within the targeted catalog entity's namespace and label selector. Net: treat as a prioritized patch for environments running the kubernetes-backend plugin with broad service-account RBAC, but it is not a drop-everything internet-facing RCE.

An authenticated Backstage user who holds the standard Kubernetes resource read permission issues a resource query through the custom resources path for Secret objects. Because redaction was not applied on that path prior to 0.21.9, the response returns the real data and stringData values instead of masked ***, disclosing cluster credentials and other confidential material. No public exploit code was identified at time of analysis, but the commit diff and tests make the mechanism trivially reproducible.