Tags: http side-channel 

Rating: 0

1. Notice strange HTTP/1.0 and HTTP/1.1 responses from 404.php
2. Guess that those values define leaking flag bits
3. Spend hours trying to recover as many bits as possible from constantly crashing server leaking random parts of the flag

Full writeup: https://github.com/p4-team/ctf/tree/master/2019-11-07-defcamp-finals/lucky