* Update on Windows WMF 0-day

Published: 2005-12-29
Last Updated: 2005-12-29 11:23:53 UTC
by Chris Carboni (Version: 1)
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From Daniel's diary entry yesterday ...

Update 19:07 UTC
: We are moving to Infocon Yellow for a bit. There has been some debate among the handlers about this step, but considering that a lot of people are on holidays and might otherwise miss the WMF 0-day problem, we have decided to raise the alert level.

The folks at Websense Labs have a nice movie on how it looks like if a system gets exploited by this WMF 0-day, see http://www.websensesecuritylabs.com/images/alerts/wmf-movie.wmv . Don't go to any of the URLs visible in the movie unless you know what you are doing (or feel like spending the next hours reinstalling your PC).

The orignal exploit site (unionseek.com) is no longer up. But the exploit is being served from various sites all over by now, see the F-Secure Blog on http://www.f-secure.com/weblog/ for an update on the versions of the exploit found in the wild.

Working exploit code is widely available, and has also been published by FRSIRT and the Metasploit Framework.

Regarding DEP (Data Execution Protection) of XPSP2, the default settings of DEP will not prevent this exploit from working. Comments we have received in the meantime suggest that if you enable DEP to cover all programs (as documented on Microsoft Technet ), the WMF exploit attempt will result in a warning and not run on its own. Don't feel too safe though, we have also received comments stating that a fully enabled DEP did not do anything good in their case.

While the original exploit only refered to the Microsoft Picture and Fax Viewer, current information is that any application which automatically displays or renders WMF files is vulnerable to the problem. This includes Google Desktop, if the indexing function finds one of the exploit WMFs on the local hard drive - see the F-Secure Weblog mentioned above for details.

Update 23:00 UTC:  The vulnerability seems to be within SHIMGVW.DLL.  Unregistering this DLL  (type REGSVR32 /U SHIMGVW.DLL at the command prompt or in the "Start->Run" Window, then reboot) will resolve most of the vulnerability, but will also break your Windows "Picture and Fax Viewer", as well as any ability of programs like "Paint" and "Explorer" to display thumbnails of any picture and real (benign) WMF files.

Update 23:19 UTC: Not that we didn't have enough "good" news already, but if you are relying on perimeter filters to block files with WMF extension from reaching your browser, you might have a surprise waiting for you. Windows XP will detect and process a WMF file based on its content ("magic bytes") and not rely on the extension alone, which means that a WMF sailing in disguise with a different extension might still be able to get you.

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