The Enable Media Replace WordPress plugin before 4.2.3 does not pass a replaced media file through the WordPress upload pipeline, so the upload prefilter that SVG-sanitizer Enable Media Replace WordPress plugin before 4.2.3 rely on never runs, allowing an authenticated user with upload access to store an SVG file containing script that executes when the file is opened directly. It requires an SVG-enabling Enable Media Replace WordPress plugin before 4.2.3 to be active, as the replace path otherwise rejects SVG uploads.