TorrentPier Deserialization of Untrusted Data vulnerability

Summary

In torrentpier/library/includes/functions.php, get_tracks() uses the unsafe native PHP serialization format to deserialize user-controlled cookies:

https://github.com/torrentpier/torrentpier/blob/84f6c9f4a081d9ffff4c233098758280304bf50f/library/includes/functions.php#L41-L60

PoC

One can use phpggc and the chain Guzzle/FW1 to write PHP code to an arbitrary file, and execute commands on the system. For instance, the cookie bb_t will be deserialized when browsing to viewforum.php.