Summary

The pr.yml GitHub workflow is vulnerable to unauthorized modification of the base repository or secrets exfiltration from a Pull Request.

Product

gpuweb/cts GitHub repository

Tested Version

The latest changeset d516cfa to the date.

Details

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

pull_request_target was introduced to allow triggered workflows to comment on PRs, label them, assign people, etc.. In order to make it possible the triggered action runner has read/write token for the base repository and the access to secrets. In order to prevent untrusted code from execution it runs in a context of the base repository.

By explicitly checking out and running 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.

on: pull_request_target: branches: - main - glsl-dependent ... - run: | git fetch origin ${{ github.event.pull_request.head.sha }} git checkout ${{ github.event.pull_request.head.sha }} - uses: actions/setup-node@v2-beta with: node-version: "15.x" - run: npm ci - run: | npm test sed -i '/out\//d' .gitignore sed -i '/out-wpt\//d' .gitignore ...

Impact

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

Coordinated Disclosure Timeline

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-2020-317 in any communication regarding this issue.