Before Windows introduced User Interface Privilege Isolation, any application could send all kinds of window messages to any window on the same desktop (a shatter attack), allowing elevation of privilege.
Now, UIPI stops low-privilege applications from sending most window messages to higher-privilege applications. Wikipedia says:
User Interface Privilege Isolation (UIPI) is a technology introduced in Windows Vista/2008 Server to combat shatter attack exploits. By making use of Mandatory Integrity Control, it prevents processes with a lower "integrity level" (IL) from sending messages to higher IL processes (except for a very specific set of UI messages).
That sounds like it ought to deal with the problem - according to this PDF linked in that article, only
WM_THEMECHANGED, and the undocumented
0x31B are allowed. (The PDF does mention a possible denial-of-service attack, starting on page 57, but while a problem, that's not elevation of privilege. I also did a cursory inspection of the DLL responsible, and it seems that on Windows 8 it doesn't actually register the message that leads to the problem.)
It doesn't look like any of those have the problem created by
WM_TIMER, which caused the target process to jump to an arbitrary address. However, this article by a Microsoft blogger (Raymond Chen) strongly insinuates that shatter attacks are still a problem:
What you can do is have a service inject the program into the session, and let it run as the logged-on user. (You have to make it run as the logged-on user in order to avoid a shatter attack.)
This Microsoft document on UAC notes that some resources "are still shared between processes at different privilege levels":
- Desktop window, which actually owns the screen surface.
- Desktop heap read-only shared memory.
- Global atom table.
Still, just having those things accessible from processes at different privilege levels wouldn't seem to allow the actual jump that causes the elevation of privilege. And even if the jump was made, I'd think that Data Execution Prevention would stop the injected code from actually being run.
So, does having a window from a process running as
SYSTEM on a low-privilege user's desktop still give that user the opportunity to elevate privileges?