Impact
The gatsby-transformer-remark plugin prior to versions 5.25.1 and 6.3.2 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 in gatsby-transformer-remark when passing input in data mode (querying MarkdownRemark 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 by or added into a file processed by gatsby-transformer-remark. The following payload demonstrates a vulnerable configuration:
---js
((require("child_process")).execSync("id >> /tmp/rce"))
---
Patches
A patch has been introduced in gatsby-transformer-remark@5.25.1 and gatsby-transformer-remark@6.3.2 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 MarkdownRemark input is attempting to use the Frontmatter engine.
Workarounds
If an older version of gatsby-transformer-remark 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.
For more information
Email us at security@gatsbyjs.com.