Coordinated Disclosure Timeline
- 2020-11-30: Report sent to maintainer
- 2020-12-01: Issue partially resolved
- 2021-03-01: Disclosure deadline reached
Summary
The pr.yml GitHub workflow is vulnerable to unauthorized modification of the base repository or secrets exfiltration from a Pull Request.
Product
s4u/pgpverify-maven-plugin GitHub repository
Tested Version
The latest changeset 87aa1b4 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:
branches:
- 'master'
...
- uses: actions/checkout@v2.3.4
with:
ref: 'refs/pull/${{ github.event.number }}/merge'
...
- run: mvn verify
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-2020-314 in any communication regarding this issue.