Actions expression injection in `filter-test-configs` (`GHSL-2023-181`)

Summary

The `pytorch/pytorch` `filter-test-configs` workflow is vulnerable to an expression injection in Actions, allowing an attacker to potentially leak secrets and alter the repository using the workflow.

### Details

The [`filter-test-configs`](https://github.com/pytorch/pytorch/blob/ec26947c586dd323d741da80008403664c533f65/.github/actions/filter-test-configs/action.yml) workflow is using the raw `github.event.workflow_run.head_branch` value inside the `filter` step:

```yaml - name: Select all requested test configurations shell: bash env: GITHUB_TOKEN: ${{ inputs.github-token }} JOB_NAME: ${{ steps.get-job-name.outputs.job-name }} id: filter run: | ... python3 "${GITHUB_ACTION_PATH}/../../scripts/filter_test_configs.py" \ ... --branch "${{ github.event.workflow_run.head_branch }}" ```

In the event of a repository using `filter-test-configs` in a `pull_request_target`-triggered workflow, an attacker could use a malicious branch name to gain command execution in the step and potentially leak secrets.

```yml name: Example

on: pull_request_target

jobs: example: runs-on: ubuntu-latest steps: - name: Filter uses: pytorch/pytorch/.github/actions/filter-test-configs@v2 ```

#### Impact

This issue may lead to stealing workflow secrets.

#### Remediation

1. Use an intermediate environment variable for potentially attacker-controlled values such as `github.event.workflow_run.head_branch`: ```yaml - name: Select all requested test configurations shell: bash env: GITHUB_TOKEN: ${{ inputs.github-token }} JOB_NAME: ${{ steps.get-job-name.outputs.job-name }} HEAD_BRANCH: ${{ github.event.workflow_run.head_branch }} id: filter run: | ... python3 "${GITHUB_ACTION_PATH}/../../scripts/filter_test_configs.py" \ ... --branch "$HEAD_BRANCH" ```

#### Resources

* [CodeQL for JavaScript - Expression injection in Actions](https://codeql.github.com/codeql-query-help/javascript/js-actions-command-injection/) * [Keeping your GitHub Actions and workflows secure Part 2: Untrusted input](https://securitylab.github.com/research/github-actions-untrusted-input/) * [Keeping your GitHub Actions and workflows secure Part 1: Preventing pwn requests](https://securitylab.github.com/research/github-actions-preventing-pwn-requests/)