In FusionPBX up to 4.5.7, the file app\messages\messages_thread.php uses an unsanitized "contact_uuid" variable coming from the URL, which is reflected on 3 occasions in HTML, leading to XSS.
https://resp3ctblog.wordpress.com/2019/10/19/fusionpbx-xss-4/
https://github.com/fusionpbx/fusionpbx/commit/c48a160af53352ad1a43518b7d0faab16b8dfbcc