Zyxel ZyWall, USG, and UAG devices allow remote attackers to inject arbitrary web script or HTML via the err_msg parameter free_time_failed.cgi CGI program, aka reflective cross-site scripting.
View the template here CVE-2019-12581.yaml
References:
https://sec-consult.com/vulnerability-lab/advisory/reflected-cross-site-scripting-in-zxel-zywall/