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March 3, 2021

GHSL-2020-246: Unauthorized repository modification or secrets exfiltration in GitHub workflows of ant-design

Jaroslav Lobacevski

Coordinated Disclosure Timeline

Summary

The ant-design/ui.yml, ant-design-pro/preview.yml and pro-components/preview.yml GitHub workflows are vulnerable to arbitrary code execution.

Product

ant-design/ant-design GitHub repository
ant-design/ant-design-pro GitHub repository
ant-design/pro-components GitHub repository

Tested Version

The latest changesets 3f126f1, e451d76 and fb2245e 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.

From preview.yml:

on:
  pull_request_target:
...
      - name: checkout
        if: github.event_name == 'pull_request_target'
        uses: actions/checkout@master
        with:
          ref: refs/pull/${{ github.event.pull_request.number }}/head
...
      - name: install
        run: npm install

From ui.yml:

on: pull_request_target
...
      - 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 install umi-plugin-pro --save
            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-2020-246 in any communication regarding this issue.