The embargo is over, so here it is: https://coderush.me/hydroph0bia-part1/
I can't stress the "NEVER USE NVRAM AS TRUSTED STORAGE" part harder, but now we all have a very nice example of a thing to not ever do, or have your SecureBoot and FW updater signing being vulnerable to all people who can set non-volatile RT variables by calling a dedicated OS API.