The TYPO3 "Content Element Selector" (ceselector) extension passes an attacker-controlled cookie directly to PHP's `unserialize()` without safely processing the input. A remote, unauthenticated attacker can supply a crafted serialized payload to trigger PHP Object Injection, leading to Remote Code Execution on the TYPO3 server. Exploitation requires the content element to be configured with `Persistent Mode: Static` in the plugin settings. This has been patched in version 3.0.3, 4.0.2, 5.0.1, and 6.0.1.