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By | John Leyden 19th February 2007 12:40

Vista security overhaul questioned

User Account Control: insecure by design?

Security researchers have taken issue with Microsoft's implementation of a security feature in Vista that is designed to stop users from routinely running systems in admin mode.

Users of Windows XP and older Microsoft operating systems habitually ran PCs in admin mode, which gives unrestricted access to the system. As a result, malware attacks carried the ability to take over compromised systems which wouldn't normally be possible if a machine was running in user mode.

The User Account Control (UAC) security functionality of Windows Vista is designed to address this problem by obliging users to run their Vista PCs via a normal user account by default. Users are asked to switch modes and enter login credentials when they request a task requiring admin credentials.

White hat hacker Joanna Rutkowska discovered that users attempting to run an installation file need to do so in admin mode. That means users are confronted with the all-or-nothing choice of granting an installed program complete system privileges or abandoning an installation altogether.

"That means that if you downloaded some freeware Tetris game, you will have to run its installer as administrator, giving it not only full access to all your file system and registry," Rutkowska writes, adding that Win XP gave her the ability to add permissions to her normal (restricted) user account that isn't possible with Vista.

Mark Russinovich, a technical fellow at Microsoft, argues in a detailed response that the design of Vista's User Account Control balances security and usability.

Rutkowska acknowledges that Microsoft has improved the security of its operating system with Vista but warns that the security shortcomings of UAC can not be so easily dismissed. "UAC is not perfect [but that] doesn't diminish the fact that it's a step in the right direction, implementing a least-privilege policy in Windows OS," she writes.

Rutkowska takes issue with Microsoft's contention that flaws in UAC controls don't in themselves create security bugs. She points, by way of example, to a security bug she has discovered which allows a low integrity level process to send WM_KEYDOWN messages to a command prompt window running at high integrity level as among the types of problems she is seeking to highlight. ®

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