Nagios XI below 5.7 is affected by code injection in the /nagiosxi/admin/graphtemplates.php component. To exploit this vulnerability, someone must have an admin user account in Nagios XI's web system.
https://www.nagios.com/downloads/nagios-xi/change-log/
https://gist.github.com/leommxj/93edce6f8572cefe79a3d7da4389374e