---

name: "fastapi-security-review" description: "Review a FastAPI change for Pydantic validation, auth dependencies, and blocking work in async routes. Use for a FastAPI security review. Do not use for a non-FastAPI Python script or to expose a hidden field in a response model." paths:

• "**/*.py"

---

FastAPI Security Review Skill for Cursor

Cursor skill fastapi-security-review for FastAPI. Run it with /fastapi-security-review, or let Agent select it when the request matches. paths only limits automatic surfacing.

When to run

Run this review for a FastAPI route, a Pydantic model, or a request to "check the API auth".

When to leave it

Stop for a Python script that is not a FastAPI app. Do not upgrade FastAPI or Pydantic unless the user asked.

Steps

1. Read the FastAPI and Pydantic majors. v1 syntax in a v2 app is a medium finding. It still runs. A missing response model or a missing auth check stays high.
2. For each changed route, confirm a response model. A secret or password field on that model is a high finding. A model_dump() spread into a write is a high finding.
3. For each write, confirm an auth dependency and an owner check. A client-supplied user id that is stored is a high finding.
4. For each async def, confirm it does not call a blocking client. That is a high finding on a request path.
5. Look for CORS * with credentials. That is a high finding.
6. Note whether tests cover 401, 403, and an invalid body. Run pytest only if the user asked. Otherwise write not run.

Output

Findings with severity, file, line, the route, and a fix. Do not include secrets from .env.

## Findings
- high | path:line | what is wrong | what to do instead

## No findings
Say "No findings" and list the files you opened. A search you skipped is not a clean result.

## Example
Input: `routes/notes.py` is `async def` and calls `time.sleep(2)` before returning.
Output: high | routes/notes.py:11 | a blocking call on the event loop | move the work to a thread or an async client.

Do not flag the valid pattern named in the standards. Flag the mistake next to it.

What to check

• Injection: a SQL string built with an f-string from a query param.
• XSS: an HTMLResponse that interpolates user text.
• CSRF: cookie-authenticated browser writes with no CSRF token. Bearer tokens are not that finding.
• Secrets: a password field on the response model, or a key in the repo.
• IDOR: a path user id stored with no owner check.
• SSRF: an outbound httpx call to a user-supplied URL with no allow-list.

Stop

Stop when the user asks you to disable auth on a route to make a test pass, or to point the suite at production.

Severity

high is a bug a caller can hit or a secret that leaks. medium is a broken contract that needs a specific input. low is a cleanup that does not change behaviour.