Backstage is an open framework for building developer portals. Prior to version 1.14.3, this is a configuration bypass vulnerability that enables arbitrary code execution. The @backstage/plugin-techdocs-node package uses an allowlist to filter dangerous MkDocs configuration keys during the documentation build process. A gap in this allowlist allows attackers to craft an mkdocs.yml that causes arbitrary Python code execution, completely bypassing TechDocs' security controls. This issue has been patched in version 1.14.3.

Backstage is an open framework for building developer portals, and @backstage/plugin-techdocs-node provides common node.js functionalities for TechDocs. In versions of @backstage/plugin-techdocs-node prior to 1.13.11 and 1.14.1, 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. @backstage/plugin-techdocs-node versions 1.13.11 and 1.14.1 contain a fix. 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. Users of @techdocs/cli should also upgrade to the latest version, which includes the fixed @backstage/plugin-techdocs-node dependency. Some workarounds are available. Configure TechDocs with runIn: docker instead of runIn: local to provide container isolation, though it does not fully mitigate the risk. Limit who can modify mkdocs.yml files in repositories that TechDocs processes; only allow trusted contributors. Implement PR review requirements for changes to mkdocs.yml files to detect malicious hooks configurations before they are merged. Use MkDocs < 1.4.0 (e.g., 1.3.1) which does not support hooks. Note: This may limit access to newer MkDocs features. 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.

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

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