Microsoft unveils shield for critical Windows flaw as attack code looms

Computerworld - With attack code that exploits a critical unpatched bug in Windows likely to go public soon, Microsoft wants users to run an automated tool that disables the vulnerable component.

The bug in SMB (Server Message Block) 2, a Microsoft-made network file- and print-sharing protocol that ships with Windows, affects Windows Vista, Windows Server 2008 and preview releases of Windows 7.

When the flaw was first disclosed Sept. 7, it was thought that attacks would only crash PCs, causing the notorious Blue Screen of Death. Since then, however, researchers have figured out how to create exploits that can be used to hijack a vulnerable computer.

Last Wednesday, Miami Beach-based Immunity, which is best known for its CANVAS penetration testing framework, built a working remote code exploit, and released it to paying subscribers of its Early Updates program.

On Friday, Microsoft confirmed that Immunity's exploit worked as advertised. "We have analyzed the code ourselves and can confirm that it works reliably against 32-bit Windows Vista and Windows Server 2008 systems," said Mark Wodrich and Jonathan Ness, both members of the Microsoft Security Response Center (MSRC) engineering team, on a company blog. "The exploit gains complete control of the targeted system and can be launched by an unauthenticated user."

More worrisome, however, was news that the open-source Metasploit pen-testing software will add attack code this week, according to HD Moore, a noted security researcher and one of Metasploit's makers. Metasploit's exploit code is often used by hackers to build malicious attacks.

According to Kostya Kortchinsky, an Immunity researcher who worked on the CANVAS attack module, the SMB 2 vulnerability is "decently wormable."

That prompted Wolfgang Kandek, the chief technology officer for security company Qualys, to implore Windows users to immediately deploy Microsoft's defensive measure. "The implementation of this workaround is now becoming critical as attackers will have access to the code soon, in the most optimistic case next week," said Kandek on Wednesday.

Microsoft has not yet set a timetable for a patch, but said it is working on a fix. "We're not slowing down our investigation, and are working on an update that can be delivered for all customers," said Wodrich and Ness. "The product team has built packages and [is] hard-at-work testing now to ensure quality."

Until a patch is ready, Microsoft recommended that users run the automated "Fix it" tool posted Friday on its support site. The tool automatically disables the SMB 2 service, rendering any attack moot. That, however, also makes it impossible for PCs to communicate to file servers and network printers using the protocol.

Microsoft has used "Fix it" tools several times this summer to help customers protect their machines until it can create and thoroughly test patches. The last time it delivered such a tool was in early July, when it issued a "Fix it" to stymie attacks against Internet Explorer 6 (IE6) and IE7.

The company's next scheduled patch day is Oct. 13, more than three weeks away, but in rare cases, Microsoft releases "out-of-band" updates, usually when it sees attacks actually under way.

So far, it hasn't found any. "We are not aware of any in-the-wild exploits or any real-world attacks," said Wodrich and Ness.

Windows Vista, Windows 2008 and Windows 7 Release Candidate (RC), the preliminary build that was handed out to millions from early May to late August, contain the SMB 2 flaw and are vulnerable to attack. Older editions, such as Windows XP, and the final version of Windows 7, dubbed RTM for "release to manufacturing," are not at risk.

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