Microsoft Patches Windows Shell Vulnerability

With the out-of-band release, Microsoft also disclosed Office documents at risk from the "no user input required" shortcut icon attack.
Image Gallery: Windows 7 Revealed
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Image Gallery: Windows 7 Revealed
Microsoft on Monday released an emergency patch against the Windows shortcut link (.LNK), aka Windows Shell, vulnerability.

All "supported" editions of Windows got a patch, "including Windows XP, Windows Vista, Windows 7, Windows Server 2008, and Windows Server 2008 R2," according to Christopher Budd, senior security response communications manager at Microsoft. He recommends companies deploy the update "as soon as possible, to help protect their computers from criminal attacks seeking to exploit the .LNK vulnerability."

In the related vulnerability announcement, Microsoft also divulged a new vector for related attacks. For the first time, it noted that "an attacker could embed an exploit in a document that supports embedded shortcuts or a hosted browser control (such as but not limited to Microsoft Office documents)."

Previously, the attack was only publicly known to work if a malicious file displayed in a Microsoft Explorer or file manager window, which would allow an attacker to remotely execute code, even if AutoRun and AutoPlay are disabled.

"This really expands the potential reach of the LNK vulnerability," wrote Sean Sullivan, a security researcher at F-Secure, on his firm's blog. "Depending on the ease to which documents can be utilized, we will now almost certainly see targeted attack attachments via e-mail messages."

The severity of the existing attacks exploiting the vulnerability was underlined by Microsoft choosing to issue the patch yesterday, rather than waiting eight more days for its typical Patch Tuesday -- the second Tuesday of the month -- patch release cycle. Indeed, multiple attacks now in circulation now target the vulnerability, including the rapidly spreading Sality family of viruses.

On the positive side, as part of Microsoft's Active Protections Program (MAPP), the company provided more detailed technical details about the attack, enabling antivirus vendors to make their signatures "more generic and effective than previously," according to Sullivan, which should help block attacks that use shortcuts embedded in Microsoft Office documents. "Kudos to Microsoft," he said.

More information on the vulnerability is available in the related Microsoft Security Advisory.

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