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February 3, 2021

GHSL-2020-327: Arbitrary code execution in dmlc/gluon-cv workflow

Jaroslav Lobačevski

Coordinated Disclosure Timeline


The ci.yml GitHub workflow is vulnerable to unauthorized modification of the base repository or secrets exfiltration from a Pull Request.


dmlc/gluon-cv GitHub repository

Tested Version

The latest changeset 1e8efef to the date.


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.

    - master
      - name: Checkout repository(For push)
        if: ${{ github.event_name == 'push' }}
        uses: actions/checkout@v2
      - name: Checkout Pull Request Repository(For pull request)
        if: ${{ github.event_name == 'pull_request' || github.event_name == 'pull_request_target' }}
        uses: actions/checkout@v2
          repository: ${{ github.event.pull_request.head.repo.full_name }}
          ref: ${{ github.event.pull_request.head.ref }}
      - name: sanity-check
        shell: bash -l {0}
        run: |
          conda env create -n gluon_cv_lint -f ./tests/pylint.yml
          conda env update -n gluon-cv-lint -f ./tests/pylint.yml --prune
          conda activate gluon-cv-lint
          conda list
          make clean
          make pylint


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


This issue was discovered and reported by GHSL team member @JarLob (Jaroslav Lobačevski).


You can contact the GHSL team at, please include a reference to GHSL-2020-327 in any communication regarding this issue.