In FusionPBX up to v4.5.7, the file app\recordings\recording_play.php uses an unsanitized "filename" variable coming from the URL, which is base64 decoded and reflected in HTML, leading to XSS.
https://resp3ctblog.wordpress.com/2019/10/19/fusionpbx-xss-16/
https://github.com/fusionpbx/fusionpbx/commit/11f2dd2254dbeb1c41bf19b8c38e8fa9bc948efb