GitHub Actions security review for workflow exploitation vulnerabilities. Use when asked to "review GitHub Actions", "audit workflows", "check CI security", "GHA security", "workflow security review", or review .github/workflows/ for pwn requests, expression injection, credential theft, and supply chain attacks. Exploitation-focused with concrete PoC scenarios.
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name
gha-security-review
description
GitHub Actions security review for workflow exploitation vulnerabilities. Use when asked to "review GitHub Actions", "audit workflows", "check CI security", "GHA security", "workflow security review", or review .github/workflows/ for pwn requests, expression injection, credential theft, and supply chain attacks. Exploitation-focused with concrete PoC scenarios.
Find exploitable vulnerabilities in GitHub Actions workflows. Every finding MUST include a concrete exploitation scenario — if you can't build the attack, don't report it.
This skill encodes attack patterns from real GitHub Actions exploits — not generic CI/CD theory.
Scope
Review the workflows provided (file, diff, or repo). Research the codebase as needed to trace complete attack paths before reporting.
Files to Review
.github/workflows/*.yml — all workflow definitions
action.yml / action.yaml — composite actions in the repo
.github/actions/*/action.yml — local reusable actions
Config files loaded by workflows: CLAUDE.md, AGENTS.md, Makefile, shell scripts under .github/
Out of Scope
Workflows in other repositories (only note the dependency)
GitHub App installation permissions (note if relevant)
Threat Model
Only report vulnerabilities exploitable by an external attacker — someone without write access to the repository. The attacker can open PRs from forks, create issues, and post comments. They cannot push to branches, trigger workflow_dispatch, or trigger manual workflows.
Do not flag vulnerabilities that require write access to exploit:
workflow_dispatch input injection — requires write access to trigger
Expression injection in push-only workflows on protected branches
workflow_call input injection where all callers are internal
Secrets in workflow_dispatch/schedule-only workflows
Confidence
Report only HIGH and MEDIUM confidence findings. Do not report theoretical issues.
Confidence
Criteria
Action
HIGH
Traced the full attack path, confirmed exploitable
Report with exploitation scenario and fix
MEDIUM
Attack path partially confirmed, uncertain link
Report as needs verification
LOW
Theoretical or mitigated elsewhere
Do not report
For each HIGH finding, provide all five elements:
Entry point — How does the attacker get in? (fork PR, issue comment, branch name, etc.)
Payload — What does the attacker send? (actual code/YAML/input)
Execution mechanism — How does the payload run? (expression expansion, checkout + script, etc.)
Impact — What does the attacker gain? (token theft, code execution, repo write access)
PoC sketch — Concrete steps an attacker would follow
If you cannot construct all five, report as MEDIUM (needs verification).
Step 1: Classify Triggers and Load References
For each workflow, identify triggers and load the appropriate reference:
Trigger / Pattern
Load Reference
pull_request_target
references/pwn-request.md
issue_comment with command parsing
references/comment-triggered-commands.md
${{ }} in run: blocks
references/expression-injection.md
PATs / deploy keys / elevated credentials
references/credential-escalation.md
Checkout PR code + config file loading
references/ai-prompt-injection-via-ci.md
Third-party actions (especially unpinned)
references/supply-chain.md
permissions: block or secrets usage
references/permissions-and-secrets.md
Self-hosted runners, cache/artifact usage
references/runner-infrastructure.md
Any confirmed finding
references/real-world-attacks.md
Load references selectively — only what's relevant to the triggers found.
Step 2: Check for Vulnerability Classes
Check 1: Pwn Request
Does the workflow use pull_request_target AND check out fork code?
Look for actions/checkout with ref: pointing to PR head
Look for local actions (./.github/actions/) that would come from the fork
Check if any run: step executes code from the checked-out PR
Check 2: Expression Injection
Are ${{ }} expressions used inside run: blocks in externally-triggerable workflows?
Map every ${{ }} expression in every run: step
Confirm the value is attacker-controlled (PR title, branch name, comment body — not numeric IDs, SHAs, or repository names)
Confirm the expression is in a run: block, not if:, with:, or job-level env:
Check 3: Unauthorized Command Execution
Does an issue_comment-triggered workflow execute commands without authorization?
Is there an author_association check?
Can any GitHub user trigger the command?
Does the command handler also use injectable expressions?
Check 4: Credential Escalation
Are elevated credentials (PATs, deploy keys) accessible to untrusted code?
What's the blast radius of each secret?
Could a compromised workflow steal long-lived tokens?
Check 5: Config File Poisoning
Does the workflow load configuration from PR-supplied files?
AI agent instructions: CLAUDE.md, AGENTS.md, .cursorrules
Build configuration: Makefile, shell scripts
Check 6: Supply Chain
Are third-party actions securely pinned?
Check 7: Permissions and Secrets
Are workflow permissions minimal? Are secrets properly scoped?
Check 8: Runner Infrastructure
Are self-hosted runners, caches, or artifacts used securely?
Safe Patterns (Do Not Flag)
Before reporting, check if the pattern is actually safe:
Any expression in workflow_dispatch/schedule/push to protected branches
Requires write access — outside threat model
Key distinction:${{ }} is dangerous in run: blocks (shell expansion) but safe in if:, with:, and env: at the job/step level (Actions runtime evaluation).
Step 3: Validate Before Reporting
Before including any finding, read the actual workflow YAML and trace the complete attack path:
Read the full workflow — don't rely on grep output alone
Trace the trigger — confirm the event and check if: conditions that gate execution
Trace the expression/checkout — confirm it's in a run: block or actually references fork code
Confirm attacker control — verify the value maps to something an external attacker sets
