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February 24, 2021

GHSL-2020-329: Unauthorized repository modification or secrets exfiltration in a GitHub workflow of Automattic/jetpack

Jaroslav Lobačevski

Coordinated Disclosure Timeline


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


Automattic/jetpack GitHub repository

Tested Version

The latest changeset 1bc2f22 to the date.


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
          ref: ${{ github.event.pull_request.head.ref }}
          repository: ${{ github.event.pull_request.head.repo.full_name }}
      - run: |
          yarn install
          yarn danger ci


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-2020-329 in any communication regarding this issue.