Summary
The release.yml GitHub workflow is vulnerable to unauthorized modification of the base repository or secrets exfiltration from a Pull Request.
Product
PureStake/moonbeam GitHub repository
Tested Version
The latest changeset 994ad70 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.
# This is only allowing pushes on the moonbeam repo or pull request.
# In the case of pull request, the CI executes the workflow from
# the commit the **PR is merging into**. This prevents malicious attack trying
# to change the CI in the PR.
####### DO NOT CHANGE THIS !! #######
on: ["push", "pull_request_target"]
...
if: ${{ github.repository == 'PureStake/moonbeam' }}
...
steps:
- name: Checkout
if: github.event_name == 'pull_request_target'
uses: actions/checkout@v2
with:
fetch-depth: 0
ref: refs/pull/${{ github.event.pull_request.number }}/merge
...
- name: Build Parachain Node
run: cargo build --release --verbose --all
Impact
The vulnerability allows for unauthorized modification of the base repository and secrets exfiltration.
Coordinated Disclosure Timeline
- 2020-11-30: Report sent to maintainers
- 2020-11-30: Maintainers acknowledges
- 2020-12-01: Issue resolved
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-2020-286 in any communication regarding this issue.