API Penetration Testing

APIs are where modern applications are most exposed — and where attackers focus their efforts. Every mobile app, single-page application, microservice, and third-party integration communicates through APIs, making them the most common entry point for data breaches in 2026. Our API penetration testing is a manual-first assessment of your REST, GraphQL, and gRPC endpoints. We test against the OWASP API Security Top 10, but our methodology goes well beyond that checklist to cover the business logic flaws, authorization gaps, and chained-request attack patterns that automated tools fundamentally cannot detect. Broken Object Level Authorization (BOLA) is the single most dangerous API vulnerability — and the one scanners are worst at finding. It occurs when an API endpoint accepts an object identifier from the user and fails to verify that the authenticated user has permission to access that specific object. A single BOLA flaw can expose every record in your database. We test every data-accessing endpoint for horizontal and vertical authorization bypass. Authentication testing covers JWT implementation security (algorithm confusion, key leakage, token expiration handling), OAuth flow manipulation, API key management, session token entropy, and credential stuffing resistance. We evaluate how your API handles expired tokens, revoked sessions, and concurrent authentication from multiple devices. Business logic testing is where manual expertise matters most. We analyze how your API handles edge cases that developers didn't anticipate: race conditions in financial transactions, discount stacking in e-commerce flows, privilege escalation through chained API calls, and workflow bypass by calling endpoints out of sequence. For GraphQL APIs, we test introspection exposure, query depth and complexity abuse (denial of service through deeply nested queries), batching attacks to bypass rate limiting, field-level authorization gaps, and subscription security through WebSocket connections. We also cover API versioning security, webhook validation and signature verification, file upload handling, pagination manipulation, and inter-service communication in microservices architectures. Critical findings are reported the moment they're confirmed — we never hold urgent vulnerabilities for the final report. Every engagement includes one round of complimentary retesting after your team implements fixes.