Mitigating the OWASP API Security Top 10

The OWASP API Security Top 10 is a curated list of the most critical security risks facing modern APIs. Unlike the classic OWASP Top 10 for web apps, this list focuses specifically on API attack surfaces — including authentication abuse, excessive data exposure, and mass assignment vulnerabilities.

FastAPI is a powerful framework, but it does not make your API secure by default. You must deliberately apply defenses at every layer: routing, validation, authentication, and serialization.

In this lesson we focus on three high-impact categories:

• API1 — Broken Object Level Authorization (BOLA)
• API2 — Broken Authentication
• API6 — Mass Assignment

Each has a distinct attack pattern and a concrete FastAPI mitigation you can apply today.

Broken Authentication (API2) occurs when an API fails to properly verify that a caller is who they claim to be. Common failure modes include:

• Accepting expired or tampered JWTs without signature verification
• Using weak or predictable secrets for token signing
• Not enforcing token expiry (exp claim)
• Allowing unlimited login attempts (no rate limiting)

In FastAPI, the most reliable pattern is to validate JWTs with a library like python-jose or PyJWT on every protected route — using a dependency injected via Depends().

The dependency approach centralises auth logic so you cannot accidentally forget it on a new route.