CVE-2026-106561 in Backstage
Summary
by MITRE • 10/07/2026
Backstage is an open framework for building developer portals. Prior to 0.21.9, the @backstage/plugin-kubernetes-backend package is affected by sensitive information disclosure in kubernetes resource queries. An authenticated user holding the standard Kubernetes resource read permission could retrieve sensitive values that the Kubernetes plugin is designed to mask, potentially exposing credentials and other confidential material held in the connected clusters. Exposure is limited to resources that the Backstage service account is permitted to read and that match the targeted catalog entity's namespace and label selector. Deployments whose cluster credentials do not grant read access to these resources are unaffected. This issue is fixed in version 0.21.9.
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Analysis
by VulDB Data Team • 10/07/2026
The vulnerability identified within the Backstage developer portal framework, specifically affecting versions prior to 0.21.9, represents a critical failure in data masking logic for Kubernetes resource queries. Backstage serves as an open platform designed to consolidate software cataloging and infrastructure management tools into a unified interface. The specific component implicated is the @backstage/plugin-kubernetes-backend package, which facilitates interaction with Kubernetes clusters. While the plugin includes mechanisms intended to obscure sensitive fields such as secrets or configuration data from end-users viewing resource details, these safeguards were found to be ineffective under certain conditions. This flaw allows for the disclosure of confidential information that should remain hidden, undermining the security posture of developer portals where visibility is often granted broadly to engineering teams while restricting access to highly privileged credentials.
From a technical perspective, the core issue lies in how the backend processes and returns Kubernetes resource data when queried through the plugin interface. Although an authenticated user possesses only standard read permissions for Kubernetes resources, which typically restricts them from directly accessing sensitive secret objects via native kubectl commands or API calls depending on RBAC policies, the Backstage application logic failed to properly filter these fields before rendering them in the UI. Consequently, when a user queries details of a deployment or other resource that references secrets or contains embedded credentials, the backend retrieves and transmits the full object structure including masked values. This indicates a server-side information disclosure vulnerability where the sanitization layer is bypassed or incomplete, allowing data intended for internal service processing to leak into the client-facing response payload.
The operational impact of this vulnerability centers on the potential exposure of sensitive credentials, API keys, and other confidential material stored within connected Kubernetes clusters. Since Backstage often integrates with multiple environments, an attacker exploiting this flaw could harvest secrets that are critical for maintaining cluster integrity or accessing downstream services. The scope of exploitation is constrained by the principle of least privilege inherent in the system design; exposure is limited to resources accessible via the specific service account configured for the Backstage instance and restricted to namespaces and label selectors matching the targeted catalog entity. Therefore, deployments where the cluster credentials do not grant read access to these sensitive resource types remain unaffected, limiting the blast radius but still posing a significant risk in environments with broad RBAC policies or poorly segmented namespaces.
This vulnerability aligns closely with CWE-209, which describes the generation of an error message that includes sensitive information about the software, the operating system, the network, or related values, although in this case it is more accurately categorized under CWE-200: Exposure of Sensitive Information to an Unauthorized Actor. In terms of adversarial tactics, this behavior corresponds to ATT&CK technique T1530, Data from Cloud Storage Object Discovery, as it involves enumerating and extracting data from cloud-native infrastructure components via API interactions. The exploitation path relies on authenticated access, placing it within the context of insider threats or compromised developer accounts rather than unauthenticated remote code execution scenarios.
To mitigate this risk, organizations running Backstage must immediately upgrade to version 0.21.9 or later where the masking logic has been corrected to ensure sensitive fields are properly stripped from responses before being sent to the client. In addition to upgrading, administrators should review their Kubernetes RBAC policies to ensure that even if such vulnerabilities exist in other integrations, the Backstage service account does not possess overly permissive access to secret objects or config maps containing high-value credentials. Implementing strict namespace isolation and regularly auditing catalog entity configurations can further reduce the attack surface by ensuring that sensitive resources are not inadvertently linked to entities visible through the developer portal interface.