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Microsoft patches new Windows bug exploited by Stuxnet

Fixes 11 flaws, reveals that July worm used four zero-days to infect PCs

September 14, 2010 04:11 PM ET

Computerworld - Microsoft today delivered nine security updates to patch 11 bugs in Office, the IIS Web server and Windows, including one that was overlooked but exploited by a July worm.

"Our old friend Stuxnet is back," said Jason Miller, data and security team manager for patch-management vendor Shavlik Technologies, referring to a worm that popped up two months as it attacked Windows computers used to manage industrial control systems in major manufacturing and utility companies.

"Vulnerability researchers decompiled the worm and found it was doing something else," Miller added.

That something else was exploiting a vulnerability in Windows' print spooler service, a fact that experts at U.S. antivirus vendor Symantec and the Russian security firm Kaspersky Lab reported to Microsoft.

Microsoft patched the print pooler software with MS10-061 today, but said two lesser zero-day vulnerabilities -- one rooted out by Kaspersky, the other by Microsoft's engineers -- will be addressed in a future update.

In early August, Microsoft shipped an emergency, or "out-of-band" update to plug a hole in Windows shortcuts, the small files displayed by icons on the desktop, on the toolbar and in the Start menu that launch applications and documents when clicked. Stuxnet had also used the shortcut bug to compromise computers.

"The fact that Stuxnet targets four previously unidentified vulnerabilities makes the worm a real standout among malware," said Alex Gostev, chief security expert with Kaspersky, in an e-mail today. "It's the first time we've come across a threat that contains so many 'surprises.'"

Other researchers echoed Gostev's new-found respect for Stuxnet's makers.

"That was a very liberal use of zero-days," noted Wolfgang Kandek, CTO at Qualys, talking about the four previously-unknown vulnerabilities the worm exploited. "I don't want to say they wasted them, but you have to wonder why someone would use four zero-days in one piece of malware. The targets must have been very important to them."

According to data compiled by Symantec in July, computers in Iran were hit hardest by Stuxnet. Siemens, whose control software was targeted by Stuxnet, today said that the worm had infected at least 14 plants.

Most researchers who Computerworld contacted today put the MS10-061 print spooler patch at the top of their to-do lists.

Andrew Storms, director of security operations at nCircle Security, was the exception.

"MS10-061 is a big deal because of its relationship to Stuxnet, but its command-and-control has been pretty much knocked out," Storms said. "It's an important item for Microsoft to fix because there exploitation is going on, but for the worm to [exploit the vulnerability] is rather mitigated."

Microsoft said that Windows XP machines sharing printers are the most vulnerable to attack.

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