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Win 7 remote kernel crasher code released

File and print freeze menace revealed

Microsoft has reportedly begun investigating a potentially nasty denial of service vulnerability affecting Windows 7.

A security bug in windows 7 and Windows 2008R2 makes it possible to lock up affected systems. The crash would happen without a Blue Screen of Death or other visible indication that anything was amiss.

The system freeze can be triggered remotely by sending malformed packets to targeted systems - specifically a NetBIOS (Network Basic Input/Output System) header that specifies an incoming SMB packet is either four bytes smaller or larger than it actually is. Server Message Block (SMB) is a network protocol used to provide shared access to files and printers.

Proof of concept code was posted by white hat security researcher Laurent Gaffié in a blog entry on Wednesday. "Whatever your firewall is set to, you can get remotely smashed via IE or even via some broadcasting nbns tricks, [with] no user interaction," Gaffié writes.

Gaffié previously highlighted flaws in Microsoft's implementation of SMB that created an even greater code execution risk back in September.

While it might be used to knock over targeted systems, there's no evidence that the latest flaw lends itself to code injection, a far more serious type of problem. News of the bug broke a day after Microsoft's regular Patch Tuesday updates came and went.

Microsoft's six patches on Tuesday included a fix (MS09-065) for a critical hole in the Windows kernel of Windows 2000, Windows XP and Windows Server 2003. The same update had an "important" (ie lesser risk) patch for Vista and Windows Server 2008. Windows 7 users were not affected by either this or two other Windows-related security updates released earlier this week.

Redmond's security gnomes have reportedly begun investigating the Windows 7 denial of service risk, but Microsoft UK was unable to shed extra light on the issue this morning. We'll update this story as and when new details emerge. ®

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