The flaw was addressed in the MS09-054 bulletin that covered "critical" holes in Microsoft's Internet Explorer but, as Redmond's Security Research & Defense team explains, the drive-by download risk extends beyond Microsoft's browser.
A browse-and-get-owned attack vector exists. All that is needed is for a user to be lured to a malicious website. Triggering this vulnerability involves the use of a malicious XBAP (XAML Browser Application). Please not that while this attack vector matches one of the attack vectors for MS09-061, the underlying vulnerability is different. Here, the affected process is the Windows Presentation Foundation (WPF) hosting process, PresentationHost.exe.
While the vulnerability is in an IE component, there is an attack vector for Firefox users as well. The reason is that .NET Framework 3.5 SP1 installs a “Windows Presentation Foundation” plug-in in Firefox.
Now, Microsoft's security folks are actually recommending that Firefox users uninstall the buggy add-on:
For Firefox users with .NET Framework 3.5 installed, you may use “Tools”-> “Add-ons” -> “Plugins”, select “Windows Presentation Foundation”, and click “Disable”.
This introduction of vulnerabilities in a competing browser is a colossal embarrassment for Microsoft. At the time of the surreptitious installs, there were prescient warnings from many in the community about the security implications of introducing new code into browsers without the knowledge -- and consent -- of end users.
This episode also underscores some of the hypocrisy that has risen to the surface in the new browser wars. When Google announced it would introduce a plug-in that runs Google Chrome inside Microsoft’s Internet Explorer, Microsoft whipped out the security card and warned that Google's move increased IE's attack surface.
“Given the security issues with plug-ins in general and Google Chrome in particular, Google Chrome Frame running as a plug-in has doubled the attach area for malware and malicious scripts. This is not a risk we would recommend our friends and families take."
Of course, when it's Microsoft introducing the security risk to other browsers (Silverlight, anyone?), we should all just grin and take it.