"utterly-deranged" was a reversing challenge during corCTF 2023. It made heavy use of opaque predicates to hinder analysis.
Developing EFI Applications in rust comes with its own challenges. Since it is a nightly feature it is susceptible to breaking. This post describes the process of fixing occuring errors and implementing a very basic EFI app.
The "Opendoor" challenge contained a Windows driver with arbitrary read and write primitives into the kernel. The goal was a privilege escalation to NT-AUTHORITY/SYSTEM in order to read the flag.txt.