How To Beat Back The New Zero-Day Windows Bug

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December 29, 2005 (2:23 PM EST)

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By Gregg Keizer , TechWeb Technology News

With a patch for the worsening zero-day Windows vulnerability perhaps weeks -- or more -- away, security companies and Microsoft on Thursday recommended workarounds and other ad hoc defenses.

Several firms, Microsoft included, told users to disable the Windows Picture and Fax Viewer, the application that Internet Explorer automatically launches to display WMF image files. Microsoft's advisory instructed users to click the Start menu, choose Run, then enter "regsvr32 -u %windir%\system32\shimgvw.dll" (without the quote marks), and click OK. Doing so, however, breaks the viewer so that it won't display other associated image file formats, such as those with the .jpg extension, a popular format used by most digital cameras.

And it might not solve the problem. "Any application which automatically displays or renders WMF files is vulnerable," wrote Chris Carboni, an analyst with the Internet Storm Center, in a blog entry Thursday.

Another tactic, said some security vendors, is to block all WMF image files at the network perimeter. Symantec, for instance, listed that advice in its latest bulletin about the vulnerability. Unfortunately, hackers can simply rename a malicious WMF file with a different extension -- .gif or .jpg, for example -- to pass through an exploit. Windows parses WMF files based not on the extension it reads, but on the content of the file, making such blocking strategies ineffective.

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