Windows Metafile Vulnerability: From Bad To Worse

Some experts say the recently announced Windows metafile vulnerability isn't so bad. However, new exploits demonstrate its unfortunate potential.

The vulnerability came to light when an exploit was discovered on a Web site. Over the New Year holiday weekend still more exploits were released into the wilds of the Internet. One exploit can be used to spawn a command shell that gives remote users dangerous access to an affected system. The exploit was developed by three apparently unscrupulous individuals and complete source code has already been posted on the Internet. Due to the way the code was developed and published, innumerable exploit variations could easily be crafted by people with little if any programming skills or knowledge of the internal workings of Windows platforms.

Another exploit unleashed over the New Year weekend attempts to take advantage of people's holiday cheer via an email message titled, "Happy New Year." The message contains an image file attachment, "HappyNewYear.jpg," which when triggered installs a backdoor. F-Secure reported the Trojan as a variant of Bifrose.

The danger of this vulnerability resides in the fact that exploits can readily be disguised as many different image file types. If a person views such a file, opens a folder containing such a file, or another program (such as search engine indexing software, or Microsoft Paint) accesses the file then the exploit would be launched in the security context of the currently logged in computer user. Compounding the problem is the fact the countless people are away enjoying the worldwide New Year holiday, which means they might not find out about the problem before they stumble into a trap centered around an exploit. Compounding the problem even further is the fact that exploits are evolving, and anti-virus and anti-spyware vendors must work relentlessly to keep up -- a difficult task at best.

For those people who are aware of the problem, there are defensive measures that can be taken. As we previously report in the news story, "Windows Graphics Rendering Vulnerability Leaves Countless Computers Unprotected ," workarounds are available. Microsoft recommends that people either enable hardware-based Data Execution Prevention (DEP) or unregister the shimgvw.dll file. As we also reported in our Security Matters blog article, "Start 2006 With A Temporary Patch?," Ilfak Guilfanov created a temporary patch that can protect systems until Microsoft releases an official patch.

On New Year's Day Tom Liston, incident response handler at the SANS Internet Storm Center (ISC), wrote "This is a bad situation that will only get worse. The very best response that our collective wisdom can create is contained in this advice - unregister shimgvw.dll and use the unofficial patch." Swa Frantzen at ISC also posted a range of IP addresses to block, which he thinks will help mitigate potential exploits.

Writing in his blog on December 31 while on holiday in Paris, Stephen Toulouse, security program manager at Microsoft, said that the Microsoft Security Response Center (MSRC) is "working to investigate this [vulnerability] and [to] provide an update so people can be protected."

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