Summary

The release-hook-on-open.yml GitHub workflow is vulnerable to unauthorized modification of the base repository or secrets exfiltration from a Pull Request.

Product

GoogleCloudPlatform/functions-framework-ruby GitHub repository

Tested Version

The latest changeset e2820fb 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: types: [opened, edited, synchronize, reopened] ... if: ${{ github.repository == 'GoogleCloudPlatform/functions-framework-ruby' }} ... - name: Checkout repo uses: actions/checkout@v2 with: ref: refs/pull/${{ github.event.pull_request.number }}/merge - name: Install Toys run: "gem install --no-document toys" - name: Check commit messages env: GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }} run: | toys release _onopen --verbose \ "--event-path=${{ github.event_path }}" \ < /dev/null

The workflow above runs the _onopen.rb ruby script from a Pull Request. There is a repository name check, but even in a case of a Pull Request from an external fork the name is still GoogleCloudPlatform/functions-framework-ruby.

Impact

The vulnerability allows for unauthorized modification of the base repository and secrets exfiltration.

Coordinated Disclosure Timeline

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-2020-283 in any communication regarding this issue.