source: http://www.securityfocus.com/bid/3159/info

A vulnerability has been discovered in Microsoft IIS that may disclose the internal IP address or internal network name to remote attackers. This vulnerability can be exploited if an attacker connects to a host using HTTPS (typically on port 443) and crafts a specially formed GET request. Microsoft IIS will return a 302 Object Moved error message containing the internal IP address or internal network name of the server.

It has been reported that a target host using HTTP is also vulnerable to this issue. 

GET /directory HTTP/1.0