SQL Injection
In Symfony HTTP Methods provided as verbs or using the override header may be treated as trusted input, but they are not validated, possibly causing SQL injection or XSS.
Deserialization of Untrusted Data
In Symfony it is possible to cache objects that may contain bad user input. On serialization or unserialization, this could result in the deletion of files that the current user has access to.
Improper Authentication
In Symfony, a vulnerability would allow an attacker to authenticate as a privileged user on sites with user registration and remember me login functionality enabled.