Stop merging vulnerable API code — automate PR security gates with Semgrep + Claude AI

Every team says "we'll fix it after the merge."
They rarely do.

I built vorsken — a GitHub Action that blocks pull requests containing
API vulnerabilities before they reach your main branch.

It combines Semgrep static analysis with Claude AI to post a plain-English
verdict directly in the PR comment: BLOCK / FLAG / PASS.

Here's how to add it to any repo in under 5 minutes.

What it does

When a PR is opened or updated:

1. Semgrep scans changed files using OWASP API Security Top 10 rules
2. Claude AI analyzes the findings and generates a human-readable report
3. A verdict is posted as a PR comment
4. A BLOCK verdict fails the required check — the merge is prevented

PR opened
└─▶ Semgrep scans with OWASP API Top10 rules
└─▶ Claude AI explains each finding in plain English
└─▶ BLOCK / FLAG / PASS posted as PR comment
└─▶ BLOCK = merge prevented ✋

text

Why not just use Semgrep alone?

Semgrep gives you rule IDs and line numbers.
vorsken adds the context developers actually need:

Setup (5 minutes)

1. Add your Anthropic API key

In your repository: Settings → Secrets → Actions → New repository secret

• Name: ANTHROPIC_API_KEY
• Value: sk-ant-...

Don't have a key yet? Get one at console.anthropic.com.

2. Create the workflow file

Create .github/workflows/policy-gate.yml:

name: Policy Gate

on:
  pull_request:
    types: [opened, synchronize, reopened]

jobs:
  gate:
    runs-on: ubuntu-latest
    permissions:
      contents: read
      pull-requests: write

    steps:
      - uses: actions/checkout@v4
        with:
          fetch-depth: 0

      - uses: zetide/vorsken@v0.2.6
        with:
          anthropic-api-key: ${{ secrets.ANTHROPIC_API_KEY }}

That's it. Push this file and open a PR.

What the PR comment looks like

When a vulnerability is detected, vorsken posts a comment like this:

🚨 vorsken Policy Gate — BLOCK

Summary: A hardcoded API key was detected in the changed files.

Rule Severity OWASP Description
hardcoded-api-key CRITICAL API8:2023 Hardcoded credential found in source.

Risk:
An attacker with read access to this repository can use the exposed
credential to authenticate as your service and access protected resources.

Fix:
Remove the hardcoded key. Read it from the environment instead:

api_key = os.environ["API_KEY"]

text

No need to look up the rule documentation — the context is right there in the PR.

OWASP API Security Top 10 coverage

vorsken ships with Semgrep rules covering all 10 OWASP API Security risks (2023 edition):

• API1 — Broken Object Level Authorization
• API2 — Broken Authentication
• API3 — Broken Object Property Level Authorization
• API4 — Unrestricted Resource Consumption
• API5 — Broken Function Level Authorization
• API6 — Unrestricted Access to Sensitive Business Flows
• API7 — Server Side Request Forgery (SSRF)
• API8 — Security Misconfiguration
• API9 — Improper Inventory Management
• API10 — Unsafe Consumption of APIs

Optional: customize the policy

Add a .stacksecai.yml to your repo root to tune the behavior:

policy:
  block_on: ["ERROR"]
  flag_on: ["WARNING"]

claude:
  model: "claude-haiku-4-5"
  severity_block: ["CRITICAL", "HIGH"]
  severity_flag: ["MEDIUM"]

rules:
  overrides:
    - rule_id: "hardcoded-password"
      action: "BLOCK"

Use your own Semgrep rules

Point semgrep-rules to your own rule directory:

- uses: zetide/vorsken@v0.2.6
  with:
    anthropic-api-key: ${{ secrets.ANTHROPIC_API_KEY }}
    semgrep-rules: ./rules/my-custom-rules

How it's built

• Semgrep — static analysis engine
• Claude API (claude-haiku-4-5) — AI analysis and plain-English output
• tenacity — exponential backoff retry on rate limits
• GitHub Actions — zero-infrastructure deployment

The action is MIT licensed. Source: github.com/zetide/vorsken

Try it now

The easiest way to see it in action:

1. Fork or clone any Python API project
2. Add the workflow file above
3. Open a PR that touches a file with a hardcoded credential or missing auth check
4. Watch the BLOCK verdict appear in the PR comment

Available on GitHub Marketplace.

Feedback and contributions welcome — if you try it out, let me know what you think in the comments.

⭐ If this looks useful, a star on GitHub helps others find it:
github.com/zetide/vorsken