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March 11, 2021

GHSL-2020-277: Unauthorized repository modification or secrets exfiltration in GitHub workflows of w3c/aria-practices

Jaroslav Lobacevski

Coordinated Disclosure Timeline

Summary

The coverage-report.yml and generate-and-commit-files.yml GitHub workflows are vulnerable to unauthorized modification of the base repository or secrets exfiltration from a Pull Request.

Product

w3c/aria-practices GitHub repository

Tested Version

The latest changesets c4d8d14 and 24efd48 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:
    paths:
    - "examples/**"
    - "test/**"
    - "!examples/landmarks/**"
...
    steps:
      - uses: actions/checkout@v2
        with:
          ref: refs/pull/${{ github.event.pull_request.number }}/head

      - name: Install dependencies
        run: npm ci

      - name: Run coverage report
        run: |
          node test/util/report.js >> coverage.log || true
...

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-2020-277 in any communication regarding this issue.