February 3, 2021

GHSL-2020-245: Arbitrary code execution in strimzi/strimzi-ui workflow

Jaroslav Lobačevski

Coordinated Disclosure Timeline

  • 2020-11-26-2020-12-12: Report sent to various maintainers.
  • 2020-12-11: No reply. Created public issue asking for security contact.
  • 2020-12-12: Report sent to the provided contact.
  • 2020-12-15: Report acknowledged.
  • 2020-12-16: Issue resolved.

Summary

The 'node-pr-jobs-secure.yml' GitHub workflow is vulnerable to arbitrary code execution.

Product

strimzi/strimzi-ui GitHub repository

Tested Version

The latest changeset 5e277d4 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.

# Running target makes it secure as this is the only way to get hold of github secrets
on: [pull_request_target]
...
      - name: Checkout PR Branch
        uses: actions/checkout@v2
        with:
          repository: ${{github.event.pull_request.head.repo.full_name}}
          ref: ${{github.event.pull_request.head.ref}}
          fetch-depth: 0
      - name: Use Node.js 14.x
        uses: actions/setup-node@v1
        with:
          node-version: 14.x
      - name: Install Dependencies and setup for CI
        run: |
          npm ci
          npm run addDevCerts
      - name: Build
        run: npm run build

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-2020-245 in any communication regarding this issue.