Coordinated Disclosure Timeline
- 2020-11-30-2020-12-01: Report sent to various maintainers.
- 2020-12-02: Report acknowledged.
- 2020-12-05: Issue resolved.
Summary
Multiple workflows are vulnerable to unauthorized modification of the base repository or secrets exfiltration from a Pull Request.
Product
deislabs/akri GitHub repository
Tested Version
The latest changeset f023a3d 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.
For example check-rust.yml:
on:
...
pull_request_target:
branches: [ main ]
paths:
- .github/workflows/check-rust.yml
- '**.rs'
- '**/Cargo.toml'
- '**/Cargo.lock'
- build/setup.sh
...
steps:
- name: Checkout the merged commit from PR and base branch
uses: actions/checkout@v2
if: github.event_name == 'pull_request_target'
with:
# pull_request_target is run in the context of the base repository
# of the pull request, so the default ref is master branch and
# ref should be manually set to the head of the PR
ref: refs/pull/${{ github.event.pull_request.number }}/head
...
- name: Install linux requirement
run: ./build/setup.sh
...
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-2020-280 in any communication regarding this issue.