Secrets Access Untrusted

Description

Workflows that pass secrets to untrusted third-party actions create extreme supply-chain risks: untrusted actions may be malicious, compromised, or contain vulnerabilities that allow secret exfiltration. Actions have access to all secrets passed to them and can log, expose, or exfiltrate credentials. Supply-chain attacks through compromised actions are a primary vector for secret theft in CI/CD pipelines. ^{1 2}

Vulnerable Instance

• Workflow passes secrets to a third-party action from an untrusted publisher.
• Action may be malicious, compromised, or contain vulnerabilities.
• Secrets can be exfiltrated by the action.

name: Build with Untrusted Action
on: [push]
jobs:
  build:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v4
      - uses: untrusted-org/some-action@v1
        with:
          api_key: ${{ secrets.API_KEY }}  # Dangerous - untrusted action

Mitigation Strategies

1. Verify action trustworthiness
   Review action source code, check publisher reputation, verify the action is from a trusted publisher, and review the action’s security history.

2. Use trusted actions
   Prefer actions from trusted publishers (actions/*, github/*) or official actions from well-known organizations. Review third-party actions thoroughly before use.

3. Minimize secret exposure
   Only pass secrets to actions that absolutely need them. Use minimal permissions for actions and consider using GitHub Apps with limited scopes.

4. Pin to commit SHA
   If you must use untrusted actions, pin to a specific commit SHA after reviewing the code. Monitor the action for updates and consider forking and maintaining your own copy.

5. Review all secret usage
   Audit all actions that receive secrets. Document why each action needs secret access and review this regularly.

6. Use environment secrets
   For sensitive operations, use environment secrets with required reviewers instead of repository secrets to add an approval gate.

Secure Version

 name: Build with Trusted Action
 on: [push]
 jobs:
   build:
     runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@v4
-      - uses: untrusted-org/some-action@v1
+      - uses: actions/setup-node@v4  # Trusted, official action
         with:
-          api_key: ${{ secrets.API_KEY }}  # Dangerous - untrusted action
+          node-version: '20'
+      - name: Use secret
+        run: |
+          curl -H "Authorization: Bearer ${{ secrets.API_KEY }}" https://api.example.com

Impact

Dimension	Severity	Notes
Likelihood		Many workflows use third-party actions, and supply-chain attacks through compromised actions are increasing.
Risk		Compromised actions can exfiltrate all secrets passed to them, enabling full system compromise and persistent access.
Blast radius		Stolen secrets can affect all systems the secrets authorize, potentially including production infrastructure, databases, and services.

References

• GitHub Docs, “Security hardening for GitHub Actions,” https://docs.github.com/en/actions/security-guides/security-hardening-for-github-actions ¹
• GitHub Docs, “Encrypted secrets,” https://docs.github.com/en/actions/security-guides/encrypted-secrets ²