The Microso ft Windows users warned about possible attacks "man-in-the-middle" capable of stealing passwords from some wireless networks and VPNs (Virtual Private Networks). However, the company will not release an update to resolve the problem.
This is not a security vulnerability that requires Microsoft to issue a security update, according to some security experts. "This issue is due to deficiencies cryptographic protocol MS-CHAP v2 and is driven by configuration changes."
Rather than release a security patch, Microsoft recommends IT administrators to add PEAP (Protected Extensible Authentication Protocol) to protect passwords on VPN sessions. A support document describes how to configure servers and clients for PEAP.
The MS-CHAP v2 is used to authenticate users based VPNs PPTP (Point-to-Point Tunneling Protocol). Windows includes an implementation of PPTP.
The threat has been identified by researcher Moxie Marlinspike safely during hacker conference Defcon. The specialist even showed a tool that could be used in this type of invasion, Chapcrack.
To use Chapcrack an attacker must first capture data packets to be transmitted via a VPN or Wi-Fi. The most likely scenario: a forgery of a legitimate point wireless, as in an airport, to find a VPN or other traffic and then attack him.
Microsoft is not aware of any attacks that have used this feature, but acknowledged that the threat is real. "An attacker who successfully exploited these weaknesses could obtain cryptographic user credentials," said the company's advisory on Monday (20/8). "These credentials could be reused to authenticate the cracker on network resources, allowing the execution of any action you take on this network."
As noted Marlinspike, MS-CHAP v2, which refers to the Windows NT SP4 and Windows 98, has been denounced as unsafe for years.