OWASP API Security Top 10, Explained With Real Findings From Our Testing

APIs have become the dominant interface for modern applications, and their security testing surface differs meaningfully from traditional web application testing. Across our API security assessments, the OWASP API Security Top 10 consistently maps to what we actually find.

Broken Object Level Authorization (BOLA) remains the most common and most severe finding — an API endpoint that checks whether a user is authenticated but not whether they're authorized to access the specific object requested, letting any authenticated user retrieve or modify another user's data simply by changing an ID in the request. We find this in roughly two-thirds of API assessments we perform.

Broken authentication follows closely, often manifesting as weak or missing rate limiting on authentication endpoints, or JWT implementations that fail to properly validate signature algorithms. Excessive data exposure — API responses returning far more fields than the client application actually uses, relying on the frontend to filter what's displayed rather than the backend to control what's sent — is nearly universal in APIs we test, and represents low-effort, high-value findings for an attacker who simply inspects raw API responses rather than the rendered UI.

The remaining categories — lack of resources and rate limiting, broken function level authorization, mass assignment, security misconfiguration, injection, improper asset management (forgotten or undocumented API versions still running in production), and unsafe consumption of third-party APIs — round out a testing methodology that treats the API as the primary attack surface, not an afterthought to web application testing. Any organization running an API-first product should budget for API-specific testing separately from traditional web app penetration testing; the finding categories and required tester expertise genuinely differ.