The Responsive Lightbox & Gallery plugin for WordPress is vulnerable to Server-Side Request Forgery in all versions up to, and including, 2.7.1. This is due to the use of `strpos()` for substring-based hostname validation instead of strict host comparison in the `ajax_upload_image()` function. This makes it possible for authenticated attackers, with Author-level access and above, to make web requests to arbitrary locations originating from the web application, which can be used to query and modify information from internal services.