In FusionPBX up to 4.5.7, the file app\extensions\extension_imports.php uses an unsanitized "query_string" variable coming from the URL, which is reflected in HTML, leading to XSS.
https://resp3ctblog.wordpress.com/2019/10/19/fusionpbx-xss-10/
https://github.com/fusionpbx/fusionpbx/commit/fc8e4e2d278ce6bffff21b04248d469a59eb8cd4