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February 3, 2021

GHSL-2020-371: Arbitrary code execution in tophat workflows

Jaroslav Lobacevski

Coordinated Disclosure Timeline

Summary

The GitHub workflows pull-request.yml in multiple branches of tophat/networkjs, tophat/commit-utils, tophat/commit-watch, tophat/sanity-runner and commit-watch.yml in tophat/commit-watch are vulnerable to unauthorized modification of the base repository or secrets exfiltration from a Pull Request.

Product

tophat/networkjs GitHub repository
tophat/commit-utils GitHub repository
tophat/commit-watch GitHub repository
tophat/sanity-runner GitHub repository

Tested Version

The latest versions to the date.

Details

Issue: Untrusted code is explicitly checked out and run on a Pull Request from a fork

Workflows triggered on pull_request_target have read/write tokens for the base repository and the access to secrets. By explicitly checking out and running the build script from a fork the untrusted code is running in an environment that is able to push to the base repository and to access secrets. More details can be found in the article Keeping your GitHub Actions and workflows secure: Preventing pwn requests.

on:
  - pull_request_target
...
        - uses: actions/checkout@v2
          with:
            ref: ${{ github.event.pull_request.head.sha }}
        - uses: ./.github/actions/detect-node
...
        - name: Install dependencies
          run: yarn install --immutable
        - name: Linting
          run: yarn lint:ci
        - name: Tests
          run: yarn test:ci
...

Impact

The vulnerability allows for unauthorized modification of the base repository and secrets exfiltration.

Credit

This issue was discovered and reported by GHSL team member @JarLob (Jaroslav Lobačevski).

Contact

You can contact the GHSL team at securitylab@github.com, please include a reference to GHSL-2020-371 in any communication regarding this issue.