LibreNMS: Stored XSS via graph_descr admin config settings echoed without escaping to all authenticated users

Summary

The graph_descr.<graphtype> family of settings is echoed verbatim without htmlspecialchars() in includes/html/pages/graphs.inc.php:194. Any admin can store a malicious HTML payload that executes in every authenticated user's browser viewing that graph type.

CVSS

CVSS:3.1/AV:N/AC:L/PR:H/UI:R/S:C/C:L/I:L/A:N — 4.8 Medium

Details

// graphs.inc.php:194
echo LibrenmsConfig::get('graph_descr.' . $vars['type']);

PoC

PUT /settings/graph_descr.device_processor
{"value": "<img src=x onerror=\"alert('ADV-15')\">"}

GET /graphs?type=device_processor
→ <img src=x onerror="alert('ADV-15')">

Fix

echo htmlspecialchars(LibrenmsConfig::get('graph_descr.' . $vars['type']), ENT_QUOTES, 'UTF-8');

Prerequisite

Admin session to set the config value.