HTTP request parsing is the step where a web server, reverse proxy, or application framework turns a raw incoming request into structured parts such as the method, path, headers, and body. It sits at the boundary between untrusted network input and application logic, so mistakes here can change how a request is understood before any security checks run.
This matters because parsing bugs can create security gaps even when the application code looks correct. Ambiguous headers, malformed encodings, or inconsistent handling of content length and chunked transfer can lead to request smuggling, routing confusion, or excessive resource use. Attackers often abuse these edge cases to bypass controls or degrade service. Defenders reduce risk by using well-tested parsers, enforcing strict protocol rules, limiting request size, and logging abnormal requests for review.