Microsoft won't fix new Windows security flaw

Gone fishin'

Microsoft says it won't be issuing a patch for a newly discovered security vulnerability in Windows that PGP's COVERT lab classifies as 'high-risk'.

The COVERT Lab issued an advisory earlier this week detailing how a local Windows networking configuration can be corrupted by redirecting the user to an arbitrary IP address of the hacker's choosing. In itself, say researchers, the vulnerability isn't destructive. For malicious crackers it's more likely to be a means to an end. But the simplicity and stealth
with which the attack can be carried out means that it merits a high risk rating, says PGP.

"All it takes is a single UDP packet sent to whoever is on the Windows network - it's unsolicited," a PGP researcher told The Register. "That person never needs to ask a question to receive an invalid response and for their cache to be corrupted, and for that machine to be the under the control of the attacker."

As an example of potential abuse, PGP's advisory cites a case where a rogue SMB (Windows' file and print network protocol) machine could be used to capture names and passwords from other users on the LAN, or over the Internet.

The problem lies in the vulnerability of a Windows' clients' NetBIOS cache. The cache contains mapping information that matches computer shares - in the Network Neighborhood or My Network Place folders - to IP addresses. Both static and dynamic entries can be modified, says the advisory.

"There's not a lot a user can do to minimize their risk," said Jim Magdych, security research manager at the lab. "Unless network administrators start blocking the traffic internally then you're still susceptible to
an attack from inside your LAN."

Home users who have a Windows-based home network attached to the Internet, and individual users who've left NetBIOS bound the IP stack in Windows, are also vulnerable. COVERT Labs advises users to unbind NetBIOS from the stack, or turn the protocol off if they're using Windows 2000.

"We've had a lot of discussion with Microsoft about it," said Magdych. "They said it would take up too much effort and be too disruptive to the Microsoft NetBIOS implementation to implement any sort of patch to correct this problem." ®

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