TL;DR (the harder way):

1. notice that s = 0 actually pass
2. attack assuming that s = 0
3. profit!

TL;DR (referenced from rbtree god):

1. hash your command and send it with your public key
2. ??
3. profit!

Original writeup (https://b6a.black/posts/2021-11-04-hacklu-crypto/#whatthehecc-198-45-solves).