OWASP API Security Top 10: A Practical 2026 Walkthrough
BOLA, mass assignment, broken auth — the most exploited API bugs in 2026, with concrete examples and remediation patterns.
BOLA (Broken Object Level Auth)
BOLA remains the #1 API risk. Most teams check authentication but skip object-level authorization, letting attackers swap an ID and read another tenant's data.
Fix it server-side: validate that the authenticated principal owns or has access to every resource ID — never trust the client.
Broken Authentication
Weak JWT validation, missing token expiry and OAuth scope confusion lead the pack. We routinely find HS256/RS256 confusion in production APIs.
Centralise auth in a single library, reject 'none' algorithms, rotate signing keys and pin allowed algorithms explicitly.
Mass Assignment
If your API accepts a JSON body and your ORM auto-binds fields, attackers will set isAdmin: true and walk in.
Use explicit allow-lists at the controller layer — never trust ORM-level binding for security boundaries.
Unrestricted Resource Consumption
Rate limiting isn't just DoS protection — it gates credential stuffing, scraping and BOLA enumeration. Apply it per-IP and per-account.
GraphQL needs query depth and complexity limits in addition to request-rate limits.
SSRF via APIs
Webhook URL fields, image-fetchers and PDF generators are SSRF goldmines. They give attackers access to cloud metadata services.
Use an allow-list of destination hosts, block private IP ranges (including IPv6) and disable HTTP redirects to private space.