TAMUctf 2021 pybox - 150 points

We spun up a server for you to execute your python code! For security reasons, we’ve disabled a few syscalls, but you can do all the computation you’d like! restricted_python/src/main.rs openssl s_client -connect tamuctf.com:443 -servername pybox -quiet

This challenge was remarkably easy. They use seccomp to disable reading from a file. That’s not nearly enough to stop a hacker from accessing a flag. They did not disable mmap, which is a pretty standard way to access a file. So standard in fact that Python has a built-in module for it. It’s that useful. Below is the exploit. Yes is was that easy. I had to determine the length of the flag by trial and error because it wouldn’t give you the flag if you asked for more than the file size.

a = open('flag.txt','rb')
x = mmap.mmap(a.fileno(), 26, flags=mmap.MAP_PRIVATE)


The flag is gigem{m3m0ry_m4pp3d_f1l35}