Impact

When TechDocs is configured with runIn: local, a malicious actor who can submit or modify a repository's mkdocs.yml file can execute arbitrary Python code on the TechDocs build server via MkDocs hooks configuration.

Patches

Upgrade to @backstage/plugin-techdocs-node version 1.13.11, 1.14.1 or later. The fix introduces an allowlist of supported MkDocs configuration keys. Unsupported configuration keys (including hooks) are now removed from mkdocs.yml before running the generator, with a warning logged to indicate which keys were removed.

Note: Users of @techdocs/cli should also upgrade to the latest version, which includes the fixed @backstage/plugin-techdocs-node dependency.

Workarounds

If you cannot upgrade immediately:

1. Use Docker mode with restricted access: Configure TechDocs with runIn: docker instead of runIn: local. This provides container isolation, though it does not fully mitigate the risk. 2. Restrict repository access: Limit who can modify mkdocs.yml files in repositories that TechDocs processes. Only allow trusted contributors. 3. Manual review: Implement PR review requirements for changes to mkdocs.yml files to detect malicious hooks configurations before they are merged. 4. Downgrade MkDocs: Use MkDocs < 1.4.0 (e.g., 1.3.1) which does not support hooks. Note: This may limit access to newer MkDocs features.

Note: Building documentation in CI/CD pipelines using @techdocs/cli does not mitigate this vulnerability, as the CLI uses the same vulnerable @backstage/plugin-techdocs-node package.

References

MkDocs Hooks Documentation MkDocs 1.4 Release Notes TechDocs Architecture

Backstage is an open platform for building developer portals. The Backstage scaffolder-backend plugin uses a templating library that requires sandbox, as it by design allows for code injection. The library used for this sandbox so far has been vm2, but in light of several past vulnerabilities and existing vulnerabilities that may not have a fix, the plugin has switched to using a different sandbox library. A malicious actor with write access to a registered scaffolder template could manipulate the template in a way that allows for remote code execution on the scaffolder-backend instance. This was only exploitable in the template YAML definition itself and not by user input data. This is vulnerability is fixed in version 1.15.0 of @backstage/plugin-scaffolder-backend.

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

Impact

The experimental OIDC provider in @backstage/plugin-auth-backend is vulnerable to a redirect URI allowlist bypass. Instances that have enabled experimental Dynamic Client Registration or Client ID Metadata Documents and configured allowedRedirectUriPatterns are affected.

A specially crafted redirect URI can pass the allowlist validation while resolving to an attacker-controlled host. If a victim approves the resulting OAuth consent request, their authorization code is sent to the attacker, who can exchange it for a valid access token.

This requires victim interaction and that one of the experimental features is explicitly enabled, which is not the default.

Patches

Upgrade to @backstage/plugin-auth-backend version 0.27.1 or later.

Workarounds

Disable experimental Dynamic Client Registration and Client ID Metadata Documents features if they are not required.

References

- RFC 6749 Section 3.1.2 - Redirection Endpoint

Impact A path traversal vulnerability in the TechDocs local generator allows attackers to read arbitrary files from the host filesystem when Backstage is configured with techdocs.generator.runIn: local.

When processing documentation from untrusted sources, symlinks within the docs directory are followed by MkDocs during the build process. File contents are embedded into generated HTML and exposed to users who can view the documentation.

Patches This vulnerability is fixed in @backstage/plugin-techdocs-node version X.X.X. Users should upgrade to this version or later.

Workarounds - Switch to runIn: docker in your app-config.yaml: yaml techdocs: generator: runIn: docker - Restrict write access to TechDocs source repositories to trusted users only

References - https://backstage.io/docs/features/techdocs/configuration