CVE-2026-32236

@backstage/plugin-auth-backend: SSRF in experimental CIMD metadata fetch

A Server-Side Request Forgery (SSRF) vulnerability exists in @backstage/plugin-auth-backend when auth.experimentalClientIdMetadataDocuments.enabled is set to true. The CIMD
metadata fetch validates the initial client_id hostname against private IP ranges but does not apply the same validation after HTTP redirects.

The practical impact is limited. The attacker cannot read the response body from the internal request, cannot control request headers or method, and the feature must be explicitly
enabled via an experimental flag that is off by default. Deployments that restrict allowedClientIdPatterns to specific trusted domains are not affected.

Patches

Patched in @backstage/plugin-auth-backend version 0.27.1. The fix disables HTTP redirect following when fetching CIMD metadata documents.

Workarounds

Disable the experimental CIMD feature by removing or setting auth.experimentalClientIdMetadataDocuments.enabled to false in your app-config. This is the default configuration.
Alternatively, restrict allowedClientIdPatterns to specific trusted domains rather than using the default wildcard pattern.

References

• IETF Client ID Metadata Document draft
• MCP Authorization Specification - Client ID Metadata Documents

Untrusted input controls the target URL of a server-initiated request, which may reach internal services not otherwise accessible from outside. Typical impact: access to internal metadata services, internal APIs, or cloud credentials.

Kodem intelligence

1. What is CVE-2026-32236? CVE-2026-32236 is a low-severity server-side request forgery (SSRF) vulnerability in @backstage/plugin-auth-backend (npm), affecting versions < 0.27.1. It is fixed in 0.27.1. Untrusted input controls the target URL of a server-initiated request, which may reach internal services not otherwise accessible from outside.
2. Which versions of @backstage/plugin-auth-backend are affected by CVE-2026-32236? @backstage/plugin-auth-backend (npm) versions < 0.27.1 is affected.
3. Is there a fix for CVE-2026-32236? Yes. CVE-2026-32236 is fixed in 0.27.1. Upgrade to this version or later.
4. Is CVE-2026-32236 exploitable, and should I be worried? Whether CVE-2026-32236 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
5. What actually determines whether CVE-2026-32236 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.
6. How do I fix CVE-2026-32236? Upgrade @backstage/plugin-auth-backend to 0.27.1 or later.