GHSA-mj46-r4gr-5x83

### 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](mailto:security@gatsbyjs.com).