OWASP API Security Top 10: A Practical Guide

The API Attack Surface

APIs are the backbone of modern applications, and they’re increasingly targeted. Unlike traditional web attacks, API vulnerabilities often stem from business logic flaws rather than technical misconfigurations.

The Top Threats

BOLA (Broken Object Level Authorization)

The most common API vulnerability. Attackers manipulate object IDs in API requests to access data belonging to other users.

# Legitimate request
GET /api/v1/users/1234/orders

# BOLA attack - accessing another user's data
GET /api/v1/users/5678/orders

Defense: Implement proper authorization checks at the object level, not just authentication at the endpoint level.

Broken Authentication

Weak authentication mechanisms, token mismanagement, and credential stuffing vulnerabilities.

Defense: Use industry-standard auth protocols, implement rate limiting, and enforce token rotation.

Excessive Data Exposure

APIs returning more data than the client needs, relying on the frontend to filter sensitive fields.

Defense: Implement response filtering at the API layer. Never trust the client to handle data sanitization.

Building Defense in Depth

Effective API security combines multiple layers: gateway-level rate limiting, schema validation, runtime protection, and continuous monitoring. No single tool solves everything.