Detecting Supply Chain Attacks In CI CD

Detecting Supply Chain Attacks in CI/CD

When to Use

• When investigating security incidents that require detecting supply chain attacks in ci cd
• When building detection rules or threat hunting queries for this domain
• When SOC analysts need structured procedures for this analysis type
• When validating security monitoring coverage for related attack techniques

Detection Gaps & Validation

• SHA-pinning checks miss tag-pinning illusions: flagging @main/@v3 is right, but a @v3 tag (or even a short SHA) is mutable/forgeable — only a full 40-char commit SHA is immutable. Also a pinned action can still pull unpinned transitive actions or docker://image:latest inside itself; recurse into reusable workflows (uses: org/repo/.github/workflows/x.yml@ref) and Dockerfile FROM lines.
• Script-injection detection is broader than github.event: untrusted input also flows through github.head_ref, github.event.pull_request.title/body, github.event.issue.*, and env: derived from them. Match the whole untrusted-context set in run: blocks, not just github.event.
• pull_request_target + checkout of PR head is the classic poisoned-pipeline RCE that YAML linting alone misses — flag workflows that combine pull_request_target with actions/checkout of the PR ref and any secret access.
• Dependency confusion isn't in the YAML: it lives in registry scope/.npmrc/pip.conf config — name-collision risk needs the package manifests, not just .github/workflows.
• Validate the scan fires: add a deliberately vulnerable test workflow (unpinned @main, run: echo ${{ github.event.issue.title }}, permissions: write-all) and confirm each rule flags it. FP tuning: first-party/org-owned actions and internal reusable workflows are lower risk — allowlist trusted orgs rather than alerting on every @-ref.

Prerequisites

• Familiarity with security operations concepts and tools
• Access to a test or lab environment for safe execution
• Python 3.8+ with required dependencies installed
• Appropriate authorization for any testing activities

Instructions

Scan CI/CD workflow files for supply chain risks by parsing GitHub Actions YAML, checking for unpinned dependencies, script injection vectors, and secrets exposure.

import yaml
from pathlib import Path

for wf in Path(".github/workflows").glob("*.yml"):
    with open(wf) as f:
        workflow = yaml.safe_load(f)
    for job_name, job in workflow.get("jobs", {}).items():
        for step in job.get("steps", []):
            uses = step.get("uses", "")
            if uses and "@" in uses and not uses.split("@")[1].startswith("sha"):
                print(f"Unpinned action: {uses} in {wf.name}")

Key supply chain risks:

1. Unpinned GitHub Actions (using @main instead of SHA)
2. Script injection via ${{ github.event }} expressions
3. Overly permissive GITHUB_TOKEN permissions
4. Third-party actions with write access to repo
5. Dependency confusion via public/private package name collision

Examples

# Check for script injection in run steps
for step in job.get("steps", []):
    run_cmd = step.get("run", "")
    if "${{" in run_cmd and "github.event" in run_cmd:
        print(f"Script injection risk: {run_cmd[:80]}")