OPNsense 19.1 Stored XSS via system_advanced_sysctl.php

OPNsense 19.1 contains a stored cross-site scripting vulnerability in the system_advanced_sysctl.php endpoint that allows attackers to inject persistent malicious scripts via the tunable parameter. Attackers can submit POST requests with script payloads that are stored and executed in the context of authenticated user sessions when the page is viewed.