The PDOSessionHandler class allows to store sessions on a PDO connection. Under some configurations (see below) and with a well-crafted payload, it was possible to do a denial of service on a Symfony application without too much resources.

An application is vulnerable when:

- It is using PDOSessionHandler to store its sessions;

- And it uses MySQL as a backend for sessions managed by PDOSessionHandler;

- And the SQL mode does not contain STRICT_ALL_TABLES or STRICT_TRANS_TABLES (check via SELECT @@sql_mode).

POC:
https://github.com/offensive-security/exploitdb-bin-sploits/raw/master/bin-sploits/44768.tgz