Microsoft patches new Windows bug exploited by Stuxnet

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

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.

But everyone agreed that a different update, MS10-062, should be patched immediately.

"We're back to media bugs," noted Miller of Shavlik. "Media and media players are very prevalent. Everyone watches video on the Web, and they may not know what they're getting themselves into."

MS10-062 patches a flaw in the MPEG-4 codec -- software that compresses and decompresses digital audio or video -- that could be used by hackers in drive-by attacks, where users' PCs are hijacked when they simply visit a malicious Web site that's serving up a malicious media file or rigged content that's streamed through a browser or other application.

Microsoft pegged MS10-061 and MS10-062 as the two updates to apply first.

Altogether, Microsoft released nine security bulletins today, four marked "critical," the most serious threat rating in its four-step scoring system. The other five were tagged "important," the second-highest ranking. The nine updates patched a total of 11 individual vulnerabilities, four of them judged critical.

Other updates called out by experts today included MS10-065, a three-patch batch for Internet Information Services (IIS), Microsoft's Web server software; and MS10-063, which patches a bug in how Windows parses OpenType fonts.

The latter is another drive-by opportunity for hackers, said Amol Sarwate, the manager of Qualys' vulnerabilities research lab.

MS10-065, on the other hand, will be of interest to hosting providers that run IIS and support PHP, said Storms. The PHP scripting language is often used to code online forums and bulletin boards, and requires the FastCGI protocol. Attackers able to locate IIS servers with FastCGI enabled could remotely hijack the machine.

"Hosting providers may not think this is critical," warned Storms, "but it is for them."

Microsoft, however, downplayed the real-world threat. "While a successful exploit leading to remote code execution is possible in theory, there are some technical factors that make it less likely," Mark Wodrich, an engineer with the Microsoft Security Response Center, said in an entry on a company blog today. "In practice, it is more likely that attacks will lead to a crash of the IIS worker process and a denial-of-service (DoS) condition when the service reaches its restart limit."

Microsoft also patched vulnerabilities in its Outlook e-mail client and the WordPad text converter for Word 97, as well as others in various protocols and subsystems within Windows.

This month's security update can be downloaded and installed via the Microsoft Update and Windows Update services, as well as through Windows Server Update Services.

Gregg Keizer covers Microsoft, security issues, Apple, Web browsers and general technology breaking news for Computerworld. Follow Gregg on Twitter at @gkeizer or subscribe to Gregg's RSS feed . His e-mail address is gkeizer@ix.netcom.com.

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