Coordinated Disclosure Timeline
- 2020-12-11: Report sent to maintainers.
- 2020-12-12: Maintainers acknowledged.
- 2021-12-14: Issue resolved.
Summary
The code-qa-sonarcloud.yml GitHub workflow is vulnerable to unauthorized modification of the base repository or secrets exfiltration from a Pull Request.
Product
a2o/snoopy GitHub repository
Tested Version
The latest changeset 37333bf 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
paths-ignore:
- '.github/*.md'
- '.github/workflows/**'
- '.gitignore'
- 'ChangeLog'
...
# In the PR-related operation mode, unlike regular github's CI workflows (where
# the workflow operates on a (preview) merge commit (as if PR was merged into the base
# branch already), we're operating on PR's HEAD (last commit of the PR) itself here.
- name: Checkout (preview) merge commit for PR ${{ github.event.pull_request.number }}
uses: actions/checkout@v2
with:
fetch-depth: 0 # Shallow clones should be disabled for a better relevancy of analysis
repository: ${{github.event.pull_request.head.repo.full_name}}
ref: ${{github.event.pull_request.head.ref}}
if: ${{ github.event_name == 'pull_request_target' }}
...
### Install build environment tools + unzip
#
- run: ./dev-tools/install-dev-software.sh
- run: DEBIAN_FRONTEND=noninteractive apt-get install -y unzip
...
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-2020-332 in any communication regarding this issue.