In Nagios XI 5.6.9, an authenticated user is able to execute arbitrary OS commands via shell metacharacters in the id parameter to schedulereport.php, in the context of the web-server user account.
In Nagios XI 5.6.9, XSS exists via the nocscreenapi.php host, hostgroup, or servicegroup parameter, or the schedulereport.php hour or frequency parameter. Any authenticated user can attack the admin user.