'Really Bad' Exploit Threatens Windows

A new exploit has been discovered in the wild that affects fully patched Windows XP SP2 systems, according to reports by security firms F-Secure and Sunbelt. The malicious code takes advantage of a vulnerability in the WMF graphics rendering engine to automatically download and install malware.

WMF, or Windows Metafile, is a vector based image format used by Microsoft's operating systems. SHIMGVW.DLL is loaded to render the images and contains a flaw that opens the door for a malformed WMF image to cause remote code execution and potentially allow for a full system compromise.

Microsoft previously fixed a vulnerability affecting WMF and EMF files in November. That problem affected Windows 2000, XP and Windows Server 2003.

"We have a number of sites that we have found with this exploit. Different sites download different spyware. We only had a handful of websites using this new exploit but now we are seeing many more using this to install bad stuff. These image files can be modified very easily to download any malware or virus," said Alex Eckelberry, CEO of Sunbelt Software.

"I hit one site with a fully patched XP system last night and it was pretty intense -- it went right through and infected my machine."

F-Secure's Mika Pehkonen warned that, "Right now, fully patched Windows XP SP2 machines are vulnerable, with no known patch." The company is detecting the offending WMF files as W32/PFV-Exploit.A, .B and .C.

"Note that you can get infected if you visit a web site that has an image file containing the exploit. Internet Explorer users might automatically get infected. Firefox users can get infected if they decide to run or download the image file," Pehkonen added.

Microsoft has been notified of the issue and it could opt to issue an emergency patch, apart from its standard Patch Tuesday security bulletins. "We expect Microsoft to issue a patch on this as soon as they can," says F-Secure.

Sunbelt's Eckelberry echoes that sentiment: "Folks, I've seen it with my own eyes and this is a really bad exploit. Be careful out there."

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