CVE-2026-32236: @backstage/plugin-auth-backend: SSRF in experimental CIMD metadata fetch
Impact 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 clientid 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
Other sources
Backstage is an open framework for building developer portals. Prior to 0.27.1, 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 clientid 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. Patched in @backstage/plugin-auth-backend version 0.27.1.
— MITRE
Affected Software
Remediation
Event History
Frequently Asked Questions
What is the severity of CVE-2026-32236?
CVE-2026-32236 is recognized as a critical Server-Side Request Forgery (SSRF) vulnerability.
How do I fix CVE-2026-32236?
To remediate CVE-2026-32236, update the affected package @backstage/plugin-auth-backend to version 0.27.1 or later.
What components are affected by CVE-2026-32236?
CVE-2026-32236 affects the @backstage/plugin-auth-backend package specifically under versions prior to 0.27.1.
What are the consequences of CVE-2026-32236?
Exploiting CVE-2026-32236 could allow unauthorized access to internal services due to SSRF vulnerabilities.
Is CVE-2026-32236 reported in any public advisories?
Yes, CVE-2026-32236 is documented in public advisories available on GitHub.