GHSL-2021-006: Arbitrary code execution in Decathlon/vitamin-web workflow

Coordinated Disclosure Timeline

• 2021-01-18: Report sent to maintainers.
• 2021-01-18: Maintainers acknowledged.
• 2021-01-18: Issue resolved.

Summary

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

Product

Decathlon/vitamin-web repository

Tested Version

The latest changeset of build-pr.yml 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:
    types: [opened, synchronize, reopened]
...
      - uses: actions/checkout@v2
        with:
          ref: refs/pull/${{ github.event.number }}/merge
...
      - name: Install dependencies
        run: yarn install --frozen-lockfile

      - name: Build
        run: yarn build

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-2021-006 in any communication regarding this issue.