How to Build a Custom Ring3 API Hook Scanner

In user-mode security, a Ring 3 API Hook Scanner is a specialized defense tool that monitors and protects the integrity of Application Programming Interface (API) calls within the lowest privilege level of the operating system. What is Ring 3?

The CPU Ring architecture separates software by privilege levels:

Ring 0 (Kernel Mode): Reserved for the OS kernel and drivers, with full access to hardware and memory.

Ring 3 (User Mode): Where standard applications (browsers, editors) run with limited system access. The Role of an API Hook Scanner

Legitimate security products, like Endpoint Detection and Response (EDR) solutions, place “hooks” in Ring 3 to intercept and analyze function calls for malicious behavior. However, malware also uses hooking to hide its presence. A scanner’s primary role is to: What is Hooking? | Huntress