Yii is an open source PHP web framework. yiisoft/yii before version 1.1.29 are vulnerable to Remote Code Execution (RCE) if the application calls `unserialize()` on arbitrary user input. An attacker may leverage this vulnerability to compromise the host system. A fix has been developed for the 1.1.29 release. Users are advised to upgrade. There are no known workarounds for this vulnerability.