I had to run make on the uncompressed folder. Perhaps the build-essential package doesn't come with NASM in Ubuntu? I'll need a bit more info on the error if you want me to try and help you :)
After extracting the POC and installing build-essential, I still get this:
nasm -O0 -felf64 -o zenleak.o zenleak.asm
make: nasm: No such file or directory
make: ** [Makefile:11: zenleak.o] Error 127
Install the nasm package. It's probably not included in build-essencial.
Thank you. I guess I should've read the error better, but I thought nasm was the thing complaining.
The parent commenter seems to have figured this out, but to clarify a bit for posterity: build-essential does not come with nasm on Ubuntu (or upstream Debian, AFAICT). It has to be installed separately for the Zenbleed PoC to compile (if not already installed).