API security testing is the systematic evaluation of application programming interfaces for vulnerabilities in authentication, authorization, data validation, business logic, and configuration. As APIs become the primary interface for modern applications -- powering mobile apps, single-page applications, microservices, and third-party integrations -- API-specific testing methodologies address the unique attack surface that traditional web application testing does not fully cover.
API security testing begins with discovery and documentation -- mapping all API endpoints, methods, parameters, and authentication mechanisms using API specifications (OpenAPI/Swagger) or traffic analysis. Authentication testing verifies token handling, session management, OAuth flow implementation, and credential policies. Authorization testing evaluates access controls by attempting to access resources across privilege levels -- testing for Broken Object Level Authorization (BOLA), Broken Function Level Authorization, and mass assignment vulnerabilities. Input validation testing submits malformed, oversized, and malicious payloads to every parameter to identify injection, type confusion, and parsing vulnerabilities. Business logic testing examines multi-step API workflows for race conditions, state manipulation, and process bypass. Rate limiting and resource consumption testing identifies endpoints vulnerable to denial of service or abuse. Configuration review checks for exposed debug endpoints, verbose error messages, CORS misconfigurations, and unnecessary HTTP methods. Schema validation testing sends requests that deviate from API specifications to identify permissive parsing. Automated API security scanners integrate with CI/CD pipelines for continuous testing of every API change.
APIs expose application functionality directly without the protective layer of a web UI that may mask or restrict certain operations. API vulnerabilities are the leading attack vector for modern application breaches. BOLA alone accounts for a significant percentage of API attacks. The OWASP API Security Top 10 highlights risks unique to APIs that generic web testing methodologies overlook.
CDA delivers API security testing through VSD Theater missions using the OWASP API Security Top 10 framework. Our methodology tests every endpoint for authorization bypass, validates that API gateways enforce security policies, and ensures API security keeps pace with rapid development cycles.