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Microsoft Warns of New Windows Vulnerability

Happy New Year! Microsoft's first Patch Tuesday for 2011 is scheduled a week from today on the 11th of January, but there's no time like the present to kick things off for the year. Microsoft has released a security advisory for a flaw in the graphics rendering engine on some versions of Windows which could be exploited to compromise vulnerable systems.

Andrew Storms, director of security operations for nCircle, e-mailed his expert commentary. "Microsoft already has an outstanding zero-day in IE, a WMI active X control bug that Secunia issued a warning about, a much bigger side story regarding ‘cross_fuzz' and, today, a new zero-day image handling bug. It's just three days into 2011 the security trend line for Microsoft doesn't look good."

The vulnerability affects the Windows Graphics Rendering Engine in Windows XP, Windows Vista, Windows Server 2003, and Windows Server 2008. According to the Microsoft security advisory, "An attacker who successfully exploited this vulnerability could run arbitrary code in the security context of the logged-on user. An attacker could then install programs; view, change, or delete data; or create new accounts with full user rights."

Anup Ghosh, founder and chief scientist, Invincea, describes the issue in more detail. "What's news is a new vulnerability appears to have been discovered in the Windows graphics rendering engine that can be exploited via a rigged .WMF image file. Since it doesn't require much user involvement (i.e. simply viewing an image) and can run arbitrary code including installing rootkits/Trojans, the vulnerability has the potential to be severe."

There are two significant silver linings. First, the current operating system releases--Windows 7 and Windows Server 2008 R2--are not impacted by this flaw. Second, even for versions of Windows that are vulnerable, there are not yet any reported attacks exploiting this flaw.

That being said, the flaw is still there and now that it is public knowledge the threat of an attack being developed goes up substantially. Microsoft notes, though--in the mitigating factors listed in the security advisory--that the vulnerability can't be exploited automatically via e-mail, stating, "For an attack to be successful, a user must open an attachment that is sent in an e-mail message."

Storms agrees, explaining, "The most likely attack scenario with this exploit is an email attachment, most likely an Office document, that contains a malformed graphic. Opening the attachment will allow the user to be exploited."

As a temporary workaround pending an actual patch or fix, Microsoft recommends modifying the access control list (ACL) for the shimgvw.dll file. The security advisory details how to go about doing so for each of the affected versions of Windows. Just be warned that modifying the ACL will result in files that are typically handled by the graphics rendering engine not displaying properly. So, you can prevent the flaw from being exploited, but you have to sacrifice the functionality of your Windows system to do it.

Microsoft is currently investigating the issue, and given the tight turnaround I would not expect to see any patch or update for this particular flaw in the January Patch Tuesday release. If the vulnerability gets turned into an automated attack, or starts to be actively used to compromise systems in the wild, it is possible that Microsoft could rush an out-of-band patch before the February Patch Tuesday, which would be February 8.

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