The issue allows remote attackers to execute arbitrary PHP code via a .php URL in the "plugins/ueditor/php/controller.php?action=catchimage" API endpoint, specifically through the `source[]` parameter, due to a lack of restrictions in inc/zzz file.php. This can be exploited by providing a URL such as "http://192.168.0.1/test.php" if the web server at 192.168.0.1 does not interpret .php files and instead sends their contents.