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.
https://owasp.org/www-community/vulnerabilities/PHP_Object_Injection
https://github.com/yiisoft/yii/security/advisories/GHSA-mw2w-2hj2-fg8q
https://github.com/yiisoft/yii/commit/37142be4dc5831114a375392e86d6450d4951c06