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December 16, 2020

GHSL-2020-247: Unauthorized repository modification or secrets exfiltration in the GitHub workflow of redwoodjs/redwood

Jaroslav Lobacevski

Summary

The ‘create_pr_package.yaml’ GitHub workflow is vulnerable to arbitrary code execution.

Product

redwoodjs/redwood GitHub repository

Tested Version

The latest changeset acb4ecf 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
...
    steps:
      - name: Checkout PR
        uses: actions/checkout@v2
        with:
          ref: ${{ github.event.pull_request.head.sha }}

      - name: Setup node
        uses: actions/setup-node@v1
        with:
          node-version: 14

      - name: Install dependencies
        run: yarn install --frozen-lockfile

      - name: Build
        run: yarn build

Impact

The vulnerability allows for unauthorized modification of the base repository and secrets exfiltration.

Coordinated Disclosure Timeline

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-2020-247 in any communication regarding this issue.