Nginx Cache Purge Preload <= 2.1.1 - Authenticated (Administrator+) Remote Code Execution

The Nginx Cache Purge Preload plugin for WordPress is vulnerable to Remote Code Execution in all versions up to, and including, 2.1.1 via the 'nppp_preload_cache_on_update' function. This is due to insufficient sanitization of the $_SERVER['HTTP_REFERERER'] parameter passed from the 'nppp_handle_fastcgi_cache_actions_admin_bar' function. This makes it possible for authenticated attackers, with Administrator-level access and above, to execute code on the server.