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March 3, 2021

GHSL-2021-008: Unauthorized repository modification or secrets exfiltration in a GitHub workflow of actions-cool/issue-helper

Jaroslav Lobacevski

Coordinated Disclosure Timeline


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


actions-cool/issues-helper GitHub repository

Tested Version

The latest changeset surge-preview.yml to the date.


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
      - uses: actions/checkout@v2
          ref: refs/pull/${{ github.event.pull_request.number }}/merge
      - uses: afc163/surge-preview@v1
          surge_token: ${{ secrets.SURGE_TOKEN }}
          github_token: ${{ secrets.GITHUB_TOKEN }}
          build: |
            yarn docs-dev:build
          dist: docs-dist
          teardown: 'true'


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


This issue was discovered and reported by GHSL team member @JarLob (Jaroslav Lobačevski).


You can contact the GHSL team at, please include a reference to GHSL-2021-008 in any communication regarding this issue.