Nagios XI versions prior to 5.11.3 are vulnerable to cross-site scripting (XSS) via the Bandwidth Report component. Insufficient validation or escaping of user-supplied input may allow an attacker to inject and execute arbitrary script in the context of a victim's browser.
Nagios addresses this vulnerability as "The Bandwidth Report component is vulnerable to a cross-site scripting attack" and "Fixed an XSS vulnerability in bandwidthreport component."