Coordinated Disclosure Timeline
- 2020-12-11: Report sent to maintainers.
- 2020-12-11: Maintainers acknowledged.
- 2021-12-15: Issue resolved.
Summary
The ci-pr.yaml GitHub workflow is vulnerable to unauthorized modification of the base repository or secrets exfiltration from a Pull Request.
Product
GoogleCloudPlatform/microservices-demo GitHub repository
Tested Version
The latest changeset 08adad9 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 should allow secret access to fork PRs (deploy tests)
pull_request_target:
branches:
- master
...
- uses: actions/checkout@v2
with:
ref: ${{github.event.pull_request.head.ref}}
repository: ${{github.event.pull_request.head.repo.full_name}}
- name: Go Unit Tests
timeout-minutes: 10
run: |
...
go test
...
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-2020-328 in any communication regarding this issue.