The Advanced Custom Fields: Extended plugin for WordPress is vulnerable to Remote Code Execution in versions 0.9.0.5 through 0.9.1.1 via the prepare_form() function. This is due to the function accepting user input and then passing that through call_user_func_array(). This makes it possible for unauthenticated attackers to execute arbitrary code on the server, which can be leveraged to inject backdoors or create new administrative user accounts.