Fuzzing API Endpoints

Fuzzing API endpoints is a reconnaissance subtechnique that involves systematically probing an application's API with various inputs to discover undocumented or hidden endpoints, parameter vulnerabilities, and authentication bypass opportunities. During the reconnaissance phase, attackers use automated tools to generate and send numerous requests with different path variations, HTTP methods, parameters, and payloads to identify anomalies in API responses that could indicate the presence of additional API functionality. This methodical approach differs from traditional directory brute-forcing by focusing specifically on API structures, often leveraging observed patterns in known endpoints to construct intelligent fuzzing sequences. Successful API fuzzing can reveal sensitive endpoints excluded from public documentation, parameter validation flaws, authorization inconsistencies, and alternative API versions, providing attackers with expanded access to application functionality or potential entry points for more advanced attacks. Modern API fuzzing techniques may incorporate machine learning to optimize request patterns based on server responses, allowing for more efficient discovery of vulnerable endpoints with fewer requests.