One User Avatar < 2.5.5 - Subscriber+ Stored XSS via 'wpua-file' Parameter

Description

The plugin is vulnerable to Stored Cross-Site Scripting via the wpua_action_process_option_update function. This is due to insufficient file type validation in wp_handle_upload() called without a MIME allow-list, with post-write validation relying on the attacker-controlled client-supplied Content-Type header rather than a server-derived type, and no cleanup of files that fail the check. This makes it possible for authenticated attackers, with subscriber-level access and above, to upload files that may be executable, which makes remote code execution possible. In order to exploit this vulnerability an admin has to give subscribers permission to upload avatars. While PHP files and svg files are rejected, dxfp files are accepted.