Drupal core contains a potential PHP Object Injection vulnerability that (if combined with another exploit) could lead to Remote Code Execution. It is not directly exploitable.
This issue is mitigated by the fact that in order for it to be exploitable, a separate vulnerability must be present to allow an attacker to pass unsafe input to `unserialize()`. There are no such known exploits in Drupal core.
To help protect against this potential vulnerability, types have been added to properties in some of Drupal core's classes. If an application extends those classes, the same types may need to be specified on the subclass to avoid a `TypeError`.
