UEFI and boot chain security are essential for the integrity of modern devices. Numerous vulnerabilities and flaws have been discovered over the years, compromising device security. In this presentation, we will provide an in-depth analysis of the Windows Boot Manager, with a particular focus on the attack surface from admin user to the UEFI environment. We will share our research methodology, setup and debugging. Additionally, we will outline our approach of fuzzing such a preliminary OS component and conclude our presentation with some of the vulnerabilities we found and general mitigations. Through this exploration, attendees will gain understanding of Secure Boot's mechanisms, the various attack surfaces at risk, and the continuous need for improvement in security practices. This knowledge is essential for defending against sophisticated boot-level attacks and ensuring the integrity of the boot process. It is an opportunity for the community to engage and learn how to deep-dive into windows boot manager.