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 strip_tags() applied) directly into $pagetitle. A single quote terminates the JS string, executing arbitrary script.Details
// LegacyController.php:75
$html .= "\ndocument.title = '$title';\n";// proxmox.inc.php:38,42
$pagetitle[] = $instance; // GET ?instance=
$pagetitle[] = $vars['vmid']; // GET ?vmid=
PoC
http://target/apps?app=proxmox&instance=%27%3Balert%28document.cookie%29%3B//Confirmed in response:
document.title = 'Apps - Proxmox - ';alert(document.cookie);// - LibreNMS';
Fix
// LegacyController.php:75
$html .= "\ndocument.title = " . json_encode($title) . ";\n";
Also wrap $instance and $vars['vmid'] in htmlspecialchars() in proxmox.inc.php.