The package gatsby-plugin-mdx before 2.14.1, from 3.0.0 and before 3.15.2 are vulnerable to Deserialization of Untrusted Data when passing input through to the gray-matter package, due to its default configurations that are missing input sanitization. Exploiting this vulnerability is possible when passing input in both webpack (MDX files in src/pages or MDX file imported as a component in frontend / React code) and data mode (querying MDX nodes via GraphQL). Workaround: If an older version of gatsby-plugin-mdx must be used, input passed into the plugin should be sanitized ahead of processing.
Affected: npm: 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.
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