Introduction to API Testing — API Discovery and Interaction

API testing has become a pivotal aspect of ensuring the security and reliability of applications. One of the critical phases in API testing is the reconnaissance, where testers identify, interact, and analyze various aspects of an API. In this blog post, we’ll delve into the intricate details of identifying API endpoints, interacting with them, and employing advanced techniques like fuzzing to uncover hidden endpoints.

Identifying API Endpoints

Browsing Applications for Additional InsightsWhile API documentation is valuable, browsing applications using the API can provide additional insights. This is particularly useful when documentation is inaccurate or outdated. Tools like Burp Scanner can crawl applications, and Burp’s browser allows manual investigation of the attack surface.Patterns and JavaScript FilesLook for patterns in the URL structure, such as /api, while browsing the application. Additionally, inspect JavaScript files, which may contain references to untriggered API endpoints.

Interacting with API Endpoints

After identifying API endpoints, interact with them using tools like Burp Repeater and Burp Intruder. This enables observation of the API’s behavior and the discovery of additional attack surface. Investigate how the API responds to changes in HTTP methods and media types to unveil potential vulnerabilities.Pay close attention to error messages and responses during API interaction, as they may contain information crucial for constructing valid HTTP requests.

Identifying Supported HTTP Methods

API endpoints support various HTTP methods, each specifying a different action on a resource. Testing all potential methods is essential to uncover additional functionality. For example, an endpoint like /api/tasksmay support GET, POST, and DELETE methods. Burp Intruder’s built-in HTTP verbs list facilitates the systematic testing of methods.

Note: Target low-priority objects when testing different HTTP methods to avoid unintended consequences.