Coordinated Disclosure Timeline

• 2020-11-30: Report sent to maintainer
• 2020-02-03: Issue fixed

Summary

The cube-ui/preview.yml and mand-mobile/preview.yml GitHub workflows are vulnerable to unauthorized modification of the base repository or secrets exfiltration from a Pull Request.

Product

didi/cube-ui repository.
didi/mand-mobile repository.

Tested Version

The latest changesets to the date: f58fd5b and 0a65333.

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
...
      - uses: actions/checkout@v2
        with:
          ref: refs/pull/${{ github.event.pull_request.number }}/merge
      - uses: afc163/surge-preview@v1
        with:
          surge_token: ${{ secrets.SURGE_TOKEN }}
          github_token: ${{ secrets.GITHUB_TOKEN }}
          build: |
            npm install
            npm run doc-demo-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 [email protected], please include a reference to GHSL-2020-265 in any communication regarding this issue.