The Ninja Forms - File Uploads plugin for WordPress is vulnerable to arbitrary file uploads due to missing file type validation in the 'NF_FU_AJAX_Controllers_Uploads::handle_upload' function in all versions up to, and including, 3.3.26. This makes it possible for unauthenticated attackers to upload arbitrary files on the affected site's server which may make remote code execution possible. Note: The vulnerability was partially patched in version 3.3.25 and fully patched in version 3.3.27.