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July 21, 2021

GHSL-2021-033: Arbitrary code execution in GitHub workflows of game-ci

Jaroslav Lobacevski

Coordinated Disclosure Timeline

Summary

The main.yml, kubernetes-tests.yml, test.yml and build-tests.yml GitHub workflows are vulnerable to arbitrary code execution.

Product

game-ci/unity-test-runner repository
game-ci/unity-builder repository
game-ci/docker repository

Tested Version

The latest changeset of main.yml, kubernetes-tests.yml, test.yml and build-tests.yml to 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 access to repository 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 access secrets. More details can be found in Keeping your GitHub Actions and workflows secure: Preventing pwn requests.

on:
  push: { branches: [main] }
  pull_request_target:
    paths-ignore:
      - ".github/**"
...
        uses: actions/checkout@v2
        if: github.event.event_type == 'pull_request_target'
        with:
          lfs: true
          ref: ${{ github.event.pull_request.head.ref }}
          repository: ${{ github.event.pull_request.head.repo.full_name }}
...
      - uses: ./
...

The action.yml file from the root directory is attacker controlled.

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-2021-033 in any communication regarding this issue.