In this blog post, we get to the heart of the matter, the actual security of the Windows Registry. I'd like to talk about what made a feature that was initially meant to be just a quick test of my fuzzing infrastructure draw me into manual research for the next 1.5 ~ 2 years, and result in Microsoft fixing (so far) 53 CVEs. I will describe the various areas that are important in the context of low-level security research, from very general ones, such as the characteristics of the codebase that allow security bugs to exist in the first place, to more specific ones, like all possible entry points to attack the registry, the impact of vulnerabilities and the primitives they generate, and some considerations on effective fuzzing and where more bugs might still be lurking.