HTTP.sys is the Windows kernel-mode component that processes HTTP requests for many server applications and web-facing services. It handles request queuing, parsing, and routing before traffic reaches user-mode code, which makes it a core part of how Windows hosts websites, APIs, and management interfaces.
Because it sits close to the network edge and often runs with high privileges, weaknesses in HTTP.sys can have a wide security impact. Attackers may target it to crash services, bypass protections, or gain code execution against exposed Windows systems. Defenders treat it as a high-priority patch area, especially on internet-facing servers, because a flaw in the HTTP processing layer can affect many services at once. Hardening usually includes timely patching, limiting exposure, and monitoring for unusual HTTP traffic or service instability.