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Dangerous Workflow Detection

Overview​

This page documents the defensive CI control that guards against risky GitHub Actions workflow patterns before merge. The control is a hybrid of two complementary parts:

  • A homegrown template-injection gate that runs in PR validation as a fast, deterministic, offline blocking check and surfaces findings in the Security tab as SARIF.
  • The Poutine supply-chain scanner, which runs as a broad advisory scanner in CI and uploads its findings to the Security tab as SARIF without blocking merge.

The homegrown gate (blocking)​

The homegrown check enforces a single, high-signal rule:

  • dangerous-workflow/template-injection
    • Triggered when attacker-controllable GitHub event values are interpolated directly into run: or github-script code execution contexts. The narrowed scope covers free-text and ref fields such as github.event.pull_request.title, github.event.pull_request.body, github.event.pull_request.head.ref, github.event.pull_request.head.label, github.event.issue.title, github.event.issue.body, github.event.comment.body, github.event.review.body, github.event.review_comment.body, github.event.discussion.title, github.event.discussion.body, github.event.head_commit.message, github.event.head_commit.author.*, github.event.commits[*].message, github.event.commits[*].author.*, github.event.workflow_run.head_branch, github.event.workflow_run.display_title, github.event.pages[*].page_name, and github.head_ref.
    • Indirect derivations through steps.*, needs.*, and env.* are intentionally out of scope to keep the rule deterministic and low-noise.

This gate is PowerShell-native, has no runtime dependencies, and runs offline as part of npm run lint:all.

Broad coverage via Poutine (advisory)​

Broader dangerous-workflow coverage is delegated to Poutine, an Apache-2.0 supply-chain scanner maintained by BoostSecurity. Poutine runs in CI and reports a wider class of issues as advisory SARIF, including:

  • Untrusted checkout / arbitrary code execution from untrusted code changes (untrusted_checkout_exec).
  • Template injection across a broader surface than the homegrown gate.
  • Unpinned or unverified third-party actions.
  • Pull-request jobs running on self-hosted runners.
  • Known vulnerabilities in build-platform components.

Poutine findings appear in the Security tab under the poutine category. They are advisory and do not block merge; the homegrown template-injection gate is the only required check.

Scope and limitations​

The split is deliberate:

  • The homegrown gate stays narrow, deterministic, and offline so it can block with near-zero false positives.
  • Poutine provides breadth and is maintained upstream, but runs advisory to avoid a noisy hard gate.
  • The # poutine:ignore untrusted_checkout_exec marker is honored by Poutine to acknowledge reviewed checkout exceptions. It does not affect the homegrown template-injection gate.
  • Taint-based expansion of the injection rule (indirect derivations) remains tracked as follow-on work.

Why this exists​

This control closes a pre-merge gap. OpenSSF Scorecard can report dangerous workflow findings, but it only runs on the default branch, so a risky workflow can reach the PR branch and merge before the repository sees the issue. The homegrown gate brings a deterministic blocking signal into PR validation, and Poutine adds broad supply-chain coverage on top.

Run it locally​

Run the homegrown gate:

npm run lint:dangerous-workflow

The command scans .github/workflows and writes results to the local logs directory. Poutine is a CI-only scanner and is not part of the offline lint pipeline.

Suppression​

Use the suppression marker only when a checkout is genuinely trusted and the exception has been reviewed. The marker is recognized by Poutine on the checkout step line itself or on the immediately preceding line:

jobs:
  build:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v4 # poutine:ignore untrusted_checkout_exec
        with:
          ref: ${{ github.ref }}

Advisory Poutine findings can also be acknowledged in .poutine.yml by rule, path, or level once triaged.

Use this only for a legitimate trusted checkout. Review expectations:

  • The checkout target must be a trusted constant or otherwise intentionally approved.
  • The comment should be added only after a human review confirms that the workflow truly needs the exception.
  • Suppressions should be temporary and removed when the workflow is refactored to a safer pattern.

Triage flow​

When the required homegrown check fails, resolve the blocking dangerous-workflow/template-injection finding:

  1. Open the failing check and read the SARIF finding for the affected workflow and line. The homegrown gate emits the stable rule ID dangerous-workflow/template-injection at level: error.
  2. Locate the run: or github-script block that interpolates an untrusted event value.
  3. Replace the interpolation with a trusted value, route the untrusted value through an intermediate env: variable, or restructure the workflow so the untrusted payload is never executed as code.
  4. Re-run npm run lint:dangerous-workflow and re-check the PR validation status.

Advisory Poutine findings such as untrusted_checkout_exec appear separately in the Security tab under the poutine category and do not block merge. Triage them by hardening the workflow or acknowledging the finding in .poutine.yml.

🤖 Crafted with precision by ✨Copilot following brilliant human instruction, then carefully refined by our team of discerning human reviewers.