Description
A critical vulnerability exists in the MagpieRSS library that is distributed with Nagios XI. This library contains a custom version of the Snoopy component which allows a remote, unauthenticated attacker to inject arbitrary arguments into a "curl" command. By requesting magpie_debug.php with a crafted value specified in the HTTP GET 'url' parameter, the vulnerable component can be exploited to write arbitrary data to a location on disk that is writable by the 'apache' user.
Remediation
Upgrade to the latest version of Nagios XI (this vulnerability was fixed in Nagios XI version 5.5.7).