`yiisoft/yii` before version 1.1.27 are vulnerable to Remote Code Execution (RCE) if the application calls `unserialize()` on arbitrary user input. This has been patched in 1.1.27.
https://github.com/yiisoft/yii/security/advisories/GHSA-442f-wcwq-fpcf
https://github.com/yiisoft/yii/commit/ed67b7cc57216557c5c595c6650cdd2d3aa41c52