A practical walkthrough of the OWASP API Security Top 10 with real-world examples, detection techniques, and remediation strategies for each vulnerability class.
The API Threat Landscape
APIs now account for over 80% of internet traffic, and they've become the primary attack surface for modern applications. The OWASP API Security Top 10 provides the definitive taxonomy of API vulnerabilities, and every category deserves dedicated testing.
What's changed since the original 2019 list: Server-Side Request Forgery (SSRF) has been elevated, unsafe consumption of third-party APIs is now a distinct category, and the emphasis on business logic flaws has intensified.
BOLA & BFLA
Broken Object-Level Authorization (BOLA) and Broken Function-Level Authorization (BFLA) remain the top two risks. BOLA allows horizontal privilege escalation (accessing other users' data); BFLA allows vertical privilege escalation (accessing admin functions as a regular user).
Testing requires multi-role, multi-tenant scenarios that traditional scanners can't orchestrate. Autonomous testing agents that maintain multiple authenticated sessions simultaneously are the most effective detection approach.
Injection & SSRF
SQL injection in APIs has evolved: GraphQL injection, NoSQL injection, and ORM-level injection are now more common than classic SQL injection. SSRF vulnerabilities allow attackers to make the server send requests to internal resources, potentially accessing cloud metadata services and internal APIs.
The most dangerous SSRF vulnerabilities chain with cloud metadata endpoints. A single SSRF in a cloud-hosted API can lead to complete infrastructure compromise.
Authentication Flaws
Broken authentication encompasses weak JWT implementations, missing token expiration, insecure password reset flows, and inadequate rate limiting on login endpoints. In API contexts, authentication flaws often involve token leakage through logs, URLs, or insecure storage.
Mass Assignment & Data Exposure
Mass assignment occurs when APIs bind client-provided data directly to internal models without filtering. An attacker adds "role": "admin" to a profile update request and escalates their privileges. Excessive data exposure returns more data than the client needs, leaking sensitive fields.
Defense-in-Depth
No single control prevents all API vulnerabilities. Effective API security combines: authentication and authorization at every endpoint, input validation and output encoding, rate limiting and throttling, comprehensive logging and monitoring, and regular adversarial testing.
Written by
Shield Research
Application Security
