Summary
The alpakka-kafka/link-validator.yml and akka-grpc/link-validator.yml GitHub workflows are vulnerable to unauthorized modification of the base repository or secrets exfiltration from a Pull Request.
Product
akka/alpakka-kafka and akka/akka-grpc GitHub repositories.
Tested Version
The latest changesets 2d8216e and ff0ad29 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, main]
...
- name: Checkout
uses: actions/checkout@v2
with:
# See https://github.com/actions/checkout/issues/299#issuecomment-677674415
ref: ${{ github.event.pull_request.head.sha }}
fetch-depth: 100
...
- name: sbt site
run: sbt docs/makeSite
...
Impact
The vulnerability allows for unauthorized modification of the base repository and secrets exfiltration.
Coordinated Disclosure Timeline
- 2020-12-11: Report sent to maintainers
- 2020-12-11: Issue fixed
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-2020-330 in any communication regarding this issue.