Microsoft changes Windows 7 UAC after new exploit code surfaces

Bug in User Account Control is now fixed, claims Microsoft, but not in beta version users have

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"To your specific point about UAC and auto-elevation," said Turner, "in the PDC build, all Windows apps can auto-elevate when you set the UAC slider to the default level. However, this won't be the case in Beta. For Beta, Windows components that can execute arbitrary code and or apps (e.g. CMD, CSCRIPT, WSCRIPT, PowerShell, etc.) are prevented from auto-elevating.

"Thus, your example won't work in the beta and beyond. This has been validated on machines running more recent builds," Turner promised.

Long, who spotted the Channel 9 thread from October and linked to it in his blog, only added, "I guess they overlooked things then."

Rivera also took exception to Microsoft's response yesterday, when the company dismissed the initial report of UAC problems. Then the pair noted that it would be easy for hackers to disable UAC without the user being any wiser, effectively ditching one of Windows most aggressively promoted security features. For its part, Microsoft downplayed that threat, with a spokesman saying, "In order for malicious code to have gotten on to the box, something else [must have] already been breached, or the user has explicitly consented."

On Vista, said Rivera, a typical home user is protected by UAC's prompts. "In this scenario, if the user has malware breach the outer layers of security -- for instance, he downloads and executes an innocent-looking e-mail attachment -- that malware is, in a general sense, confined to the permissions that user has.

"I understand 'something else' has to be breached.... I hear Microsoft loud and clear here," said Rivera. "The problem I have is that in Windows 7, this same user in the same scenario can have malware that can break its confinement to do administrative-level damage to the machine."

That, he said, pertains to both possible UAC attack avenues: the earlier one that disabled the feature and the newer one, which lets malware hoodwink UAC into thinking it's safe code.

The solution, said Rivera, is for Microsoft to revert UAC to its Vista behavior. "I understand some believe we're in a 'damned if you do, damned if you don't' dilemma," he said. "I can see where they're coming from. My personal feeling is to ship with UAC configured to behave like Windows Vista by default. It's a hard problem that won't be solved overnight."

But Microsoft's not going to take Rivera's advice. Late Wednesday, a spokesman said that the company had addressed the latest UAC concerns in post-beta builds of Windows 7. "No, Microsoft has not reverted Windows 7 UAC's behavior to mimic Windows Vista," the spokesman said in response to several follow-up questions.

He also downplayed the threat to people who have downloaded and installed the Windows 7 beta since its public launch on Jan. 10. "We are not aware of anyone impacted by this issue at this time," the spokesman added.

Assuming Microsoft has closed the hole, the first time that most users will be able to obtain a patched or modified UAC will be when the company delivers the Windows 7 release candidate (RC). Although it has not set a timetable for that release, the head of Windows engineering last week confirmed that the operating system is moving directly to that milestone from beta.

In the meantime, Rivera and Long have recommended that users change Windows 7's UAC setting to the "Always notify" option.

Copyright © 2009 IDG Communications, Inc.

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