

It’s called a Path Traversal attack.
Basically, if you add a …/ in a query, you can start to work backwards in the directory tree to root, then go up again to someplace you shouldn’t go. The firewall doesn’t block this attack, cause it’s just doing a regular HTTP(s) request.






The point of the comic is that people expect a firewall to protect them from attacks, but then the attack comes in as a path traversal and the firewall does nothing.