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March 3, 2021

GHSL-2020-267: Unauthorized repository modification or secrets exfiltration in GitHub workflows of Antvis repositories

Jaroslav Lobacevski

Coordinated Disclosure Timeline

Summary

Multiple antvis GitHub workflows are vulnerable to unauthorized modification of the base repository or secrets exfiltration from a Pull Request.

Product

Antvis repositories.

Tested Version

The latest changesets to the date: f1c7b6b, 4111b2b, adf6849, e104920, f586a0a and 96c842f.

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

jobs:
  preview:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v2
        with:
          ref: refs/pull/${{ github.event.pull_request.number }}/merge
      - uses: afc163/surge-preview@v1
        with:
          surge_token: ${{ secrets.SURGE_TOKEN }}
          github_token: ${{ secrets.GITHUB_TOKEN }}
          build: |
            npm install
            npm run build
          dist: public

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-2020-267 in any communication regarding this issue.