LibreNMS: Reflected XSS via Proxmox instance/vmid GET parameters injected into document.title JavaScript assignment

Summary LegacyController.php:75 writes the page title into a document.title JS assignment using string interpolation. apps/proxmox.inc.php pushes $vars'instance' and $vars'vmid' GET params, only striptags applied directly into $pagetitle. A single quote terminates the JS string, executing arbitra...