TorrentPier is an open source BitTorrent Public/Private tracker engine, written in php. In torrentpier/library/includes/functions.php, get_tracks() uses the unsafe native PHP serialization format to deserialize user-controlled cookies. 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. This issue has been addressed in commit ed37e6e52 which is expected to be included in release version 2.4.4. Users are advised to upgrade as soon as the new release is available. There are no known workarounds for this vulnerability.
The product deserializes untrusted data without sufficiently verifying that the resulting data will be valid.
It is often convenient to serialize objects for communication or to save them for later use. However, deserialized data or code can often be modified without using the provided accessor functions if it does not use cryptography to protect itself. Furthermore, any cryptography would still be client-side security – which is a dangerous security assumption. Data that is untrusted can not be trusted to be well-formed. When developers place no restrictions on “gadget chains,” or series of instances and method invocations that can self-execute during the deserialization process (i.e., before the object is returned to the caller), it is sometimes possible for attackers to leverage them to perform unauthorized actions, like generating a shell.