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Microsoft patches critical IE, Silverlight drive-by bugs

Fixes 23 flaws, including one that also affects Mac users running Silverlight plug-in

October 11, 2011 04:27 PM ET

Computerworld - Microsoft today shipped eight security updates that patched 23 vulnerabilities in Windows, Internet Explorer (IE), .Net Framework, Silverlight and other bits in its portfolio.

Two of the updates were labeled "critical," Microsoft's most-serious threat ranking, while the other six were rated "important," the next-most-severe tag.

All but eight of the vulnerabilities -- which were tagged to IE -- affected one or more editions of Microsoft's client or server versions of Windows. Of the 23 total bugs, nine were rated critical, 13 were pegged important and one was marked "moderate."

The two critical updates -- MS11-081 for IE, and MS11-078 for .Net and Silverlight -- were the two called out by Microsoft and consistently by outside researchers as the pair to apply first.

"It's no surprise that IE is at the top of the list," said Storms. Microsoft typically patches its browser every other month, and last updated IE in August.

One of the eight critical vulnerabilities in the IE update affected just IE9, which shipped last March. Microsoft has patched IE9 before today, but this is the first it's needed to fix a flaw specific to only that edition.

The IE9-only vulnerability is in that edition's version of a JavaScript DLL (dynamic link library) used by that browser.

As usual, the IE vulnerabilities could be exploited by hackers with a classic "drive-by download" style of attack simply by convincing users to steer for a malicious website.

Other researchers agreed that MS11-081 should be deployed immediately. "Every time you see one of these [IE] updates, you need to patch them immediately," said Jason Miller, of VMware's research and development team.

The second consensus top-pick was the update for .Net -- a Windows-centric software framework -- and Silverlight, a Microsoft application framework for content-intensive websites and online applications.

Like the IE update, MS11-078 can be exploited by attackers who dupe users into visiting a malicious website. Worse, the flaw could be exploited by hackers targeting not just IE users, but Mac owners running a browser with the Silverlight plug-in, or Windows users running the plug-in within Apple's Safari, Google's Chrome or Mozilla's Firefox.

"By my reading of the bulletin, it's cross-browser and cross-platform," said Miller.

Microsoft updated its Mac Silverlight plug-in separately; users should immediately download and install the newest version from the Silverlight website.

Storms highlighted MS11-078 if only because of its novelty. "We're used to the IE bugs, but [MS11-078] has three different attack vectors, and the Web hosting one has high potential for exploitation," Storms said.

"If a Web hosting environment allows users to upload custom ASP.NET applications, an attacker could upload a malicious ASP.NET application that uses this vulnerability to break out of the sandbox used to prevent ASP.NET code from performing harmful actions on the server system," said Microsoft in its accompanying bulletin.

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