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.
The product constructs all or part of a code segment using externally-influenced input from an upstream component, but it does not neutralize or incorrectly neutralizes special elements that could modify the syntax or behavior of the intended code segment.