Better Messages < 2.15.20 - Authenticated (Administrator+) Arbitrary File Deletion via Path Traversal via 'file' Parameter

Description

The Better Messages – Chat Rooms, Group Chat, Private Messages & AI Chat Bots plugin for WordPress is vulnerable to arbitrary file deletion due to insufficient file path validation in the delete_sticker function in all versions up to, and including, 2.15.19. This makes it possible for authenticated attackers, with administrator-level access and above, to delete arbitrary files on the server, which can easily lead to remote code execution when the right file is deleted (such as wp-config.php). The prefix check intended to restrict deletion to the uploads directory can be bypassed by crafting a URL that begins with the legitimate uploads base URL but embeds ../ traversal sequences in the path portion, as the normalize_sticker function only applies esc_url_raw(), which does not strip ../ sequences, allowing the traversal payload to be stored verbatim in WordPress options.