In Yii Framework 2.x before 2.0.14, remote attackers could obtain potentially sensitive information from exception messages, or exploit reflected XSS on the error handler page in non-debug mode. Related to base/ErrorHandler.php, log/Dispatcher.php, and views/errorHandler/exception.php.
https://github.com/yiisoft/yii2/pull/15534
https://github.com/yiisoft/yii2/issues/14711
https://github.com/yiisoft/yii2/commit/6b0be47e0fa9c532e03b07b4369050582fcf5c7a