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Hackers have posted attack code for what appears to be a zero-day vulnerability in Microsoft Works, the productivity software suite aimed at small businesses and home offices.
The basic details, via McAfee analyst Kevin Beets:
“The flaw lies in an ActiveX component of Microsoft Works Image Server (WkImgSrv.dll). Yes, it appears successful exploitation would allow for code execution via a controlled pointer. For this to occur, the victim would need to visit a malicious Web site.“
I found this Milw0rm proof-of-concept referencing that ActiveX control that causes a Windows host to crash. A working exploit that does more damage (heap spraying to execute code) is also publicly available.
On the plus side, Beets said the buggy ActiveX control is not marked safe, meaning that exploit attempts will trigger an IE warning.
“Initial testing on Windows XP SP2 + Internet Explorer 7 shows this to be easily exploitable once past the ‘warning’ hurdle,” Beets warned.
Even so, Microsoft Works users should consider setting the kill bit for clsid:00E1DB59-6EFD-4CE7-8C0A-2DA3BCAAD9C6 to help mitigate a potential attack.
Microsoft offers instructions on how to block an ActiveX control from running in Internet Explorer, but this should be done carefully because it involves editing registry keys, a sensitive part of the operating system.
WinPatrol offers a tool that offers users a point-and-click interface for monitoring and controlling ActiveX components on Windows machines.
I’ve pinged Microsoft for confirmation on this. Will update this post as necessary.
UPDATE: Microsoft responded with the standard “we’re investigating” language:
“Microsoft is investigating new public claims of a vulnerability in an ActiveX control in Microsoft Works and is aware of detailed public exploit code was published on the Internet. We’re currently unaware of any attacks trying to use the claimed vulnerability or of customer impact. Once the company is done investigating, it will take appropriate action to help protect customers. This may include providing a security update through the monthly release process, an out-of-cycle update or additional guidance to help customers protect themselves.“