Unsanitized JavaScript code injection possible in gatsby-plugin-mdx

Impact

The gatsby-plugin-mdx plugin prior to versions 3.15.2 and 2.14.1 passes input through to the gray-matter npm package, which is vulnerable to JavaScript injection in its default configuration, unless input is sanitized. The vulnerability is present when passing input in both webpack (MDX files in src/pages or MDX file imported as component in frontend / React code) and data mode (querying MDX nodes via GraphQL). Injected JavaScript executes in the context of the build server.

To exploit this vulnerability untrusted/unsanitized input would need to be sourced or added into an MDX file. The following MDX payload demonstrates a vulnerable configuration:

---js
((require("child_process")).execSync("id >> /tmp/rce"))
---

Patches

A patch has been introduced in gatsby-plugin-mdx@3.15.2 and gatsby-plugin-mdx@2.14.1 which mitigates the issue by disabling the gray-matter JavaScript Frontmatter engine. The patch introduces a new option, JSFrontmatterEngine which is set to false by default. When setting JSFrontmatterEngine to true, input passed to gatsby-plugin-mdx must be sanitized before processing to avoid a security risk. Warnings are displayed when enabling JSFrontmatterEngine to true or if it appears that the MDX input is attempting to use the Frontmatter engine.

Workarounds

If an older version of gatsby-plugin-mdx must be used, input passed into the plugin should be sanitized ahead of processing.

We encourage projects to upgrade to the latest major release branch for all Gatsby plugins to ensure the latest security updates and bug fixes are received in a timely manner.

Credits

We would like to thank Snyk [snyk.io] for initially bringing the issue to our attention, as well as Feng Xiao and Zhongfu Su, who reported the issue to Snyk.

For more information

Email us at security@gatsbyjs.com.