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Microsoft patches critical Outlook drive-by bug

Also ships first fix for 'DLL load hijacking' flaw in Office 2007/2010 as part of 11-patch security update

November 9, 2010 04:11 PM ET

Computerworld - Microsoft today patched 11 vulnerabilities, including one in Office that hackers will quickly exploit to launch drive-by attacks, said security experts.

As expected, Microsoft did not ship a fix for the flaw in Internet Explorer (IE) that criminals are currently using to hijack Windows PCs.

Of the 11 flaws addressed in three separate updates, only one was pegged as "critical," Microsoft's top ranking in its four-step scoring system. The remaining 10 were all marked "important," the second-highest rating.

"The one that gives me the heebie-jeebies this month is the Office update," said Andrew Storms, director of security operations at nCircle Security. "The RTF vulnerability can be triggered simply by viewing a message in Outlook, so all you have to do is receive a [malicious] message. Then the game is over."

Storms was referring to MS10-087, a five-patch update for Office XP, 2003, 2007 and 2010 on Windows, and Office for Mac 2004, 2008 and 2011.

The only critical bug this month is in the RTF (rich text format) parser within Outlook, the e-mail client packaged with Office. "The vulnerability could be exploited when the specially crafted RTF e-mail message is previewed or opened in Outlook," Microsoft's advisory stated.

"That's a classic drive-by," echoed Amol Sarwate, manager of Qualys' vulnerabilities research lab.

Both Office 2007 and Office 2010, Microsoft's two newest suites, can be exploited using drive-by attacks launched against Outlook. Today's patch was the first critical update for Office 2010, which launched only in June.

Other researchers, including Microsoft's own security team, said that the RTF flaw was the most serious of the month's bugs, and urged users to patch pronto.

"This is one that requires no user interaction," said Jason Miller, the data and security team manager for Shavlik Technologies. "RTF is a common document format like PDF that's not blocked by firewalls or at the e-mail gateway. Once a [malformed] message hits the Outlook preview pane, remote code can be executed. You should patch this right away."

Because the RTF vulnerability doesn't require the user to do anything other than to preview a message, it will probably be exploited almost immediately by attackers, said Miller.

Microsoft patched a similar vulnerability in RTF document parsing in August with MS10-056. In that bulletin, the company labeled one of two RTF-related bugs as critical in Office 2007.

The MS10-087 update also included the first fix by Microsoft for the "DLL load hijacking" or "binary planting" vulnerability class that researchers disclosed last summer. Office 2007 and Office 2010 were both patched to protect users from DLL load hijacking attacks.

In mid-August, noted vulnerability researcher HD Moore announced that he'd uncovered scores of Windows applications that didn't call code libraries -- dubbed "dynamic-link library," or "DLL" -- using the full path name, but instead used only the file name, giving hackers an attack window if they were able to trick an application into loading a malicious file with the same name as a required DLL.

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