In yiisoft/yii2 version 2.0.48, the base Component class contains a vulnerability where the __set() magic method does not validate that the value passed is a valid Behavior class name or configuration. This allows an attacker to instantiate arbitrary classes, passing parameters to their constructors and invoking setter methods. Depending on the installed dependencies, various types of attacks are possible, including the execution of arbitrary code, retrieval of sensitive information, and unauthorized access.
The product uses external input with reflection to select which classes or code to use, but it does not sufficiently prevent the input from selecting improper classes or code.