GHSL-2020-367: Arbitrary code execution in android-password-store/Android-Password-Store workflow

Coordinated Disclosure Timeline

• 2020-12-21: Report sent to maintainers.
• 2020-12-22: Maintainers acknowledged.
• 2020-12-22: Issue resolved.

Summary

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

Product

android-password-store/Android-Password-Store GitHub repository

Tested Version

The latest changeset 67393ef 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]
...
      - name: Checkout code (pull_request)
        if: github.event_name == 'pull_request' || github.event_name == 'pull_request_target'
        uses: actions/checkout@v2
        with:
          ref: 'refs/pull/${{ github.event.number }}/merge'
...
    - name: Checkout repository
      if: ${{ steps.service-changed.outputs.result == 'true' }}
      uses: actions/checkout@5a4ac9002d0be2fb38bd78e4b4dbde5606d7042f
      with:
        ref: refs/pull/${{ github.event.pull_request.number }}/merge
...
    - name: Run unit tests
      if: ${{ steps.service-changed.outputs.result == 'true' }}
      uses: burrunan/gradle-cache-action@03c71a8ba93d670980695505f48f49daf43704a6
      with:
        arguments: apiCheck testFreeDebug lintFreeDebug
...

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-2020-367 in any communication regarding this issue.