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 'nppppreloadcacheonupdate' function. This is due to insufficient sanitization of the $SERVER['HTTPREFERERER'] parameter passed from the 'nppphandlefastcgicacheactionsadminbar' function. This makes it possible for authenticated attackers, with Administrator-level access and above, to execute code on the server.