Coordinated Disclosure Timeline
- 2020-12-11: Issue reported to maintainers
- 2020-12-11: Report acknowledged
- 2020-12-11: Issue resolved
Summary
The dangerci.yml GitHub workflow is vulnerable to unauthorized modification of the base repository or secrets exfiltration from a Pull Request.
Product
Automattic/jetpack GitHub repository
Tested Version
The latest changeset 1bc2f22 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
env:
DANGER_GITHUB_API_TOKEN: ${{ secrets.DANGER_TOKEN }}
...
- uses: actions/checkout@v2
with:
ref: ${{ github.event.pull_request.head.ref }}
repository: ${{ github.event.pull_request.head.repo.full_name }}
...
- run: |
yarn install
yarn danger ci
...
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-2020-329 in any communication regarding this issue.