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Blogger Long Zheng of Started Something has published a proof-of-concept attack of how to use a script to easily disable the Windows UAC, do to the inherent design flaw that it trusts changes to itself blindly. Microsoft thus far has refused to acknowledge that it needs to fix the problem calling it "by design" and yanking a MSDN blog on the UAC changes.  (Source: Started Something)
Microsoft insists big Windows 7 security hole will not be fixed, is "by design"

When Windows Vista was launched, it brought to the table a new feature that was supposed to safeguard the user:  the User Account Control (UAC).  However, the useful feature, which could be disabled, became the source of a great deal of the OS's early criticism due its warning messages which some users found irritating.

With Windows 7, Microsoft decided to switch gears and is offering a less nosey UAC in the beta version of the OS.  This move was the subject to much early praise.  However, it may have now backfired as a blogger Long Zheng, who runs the blog Start Something, has detailed a proof-of-concept attack against the new Windows 7 UAC.

Mr. Zheng says the attack is a vindication of Windows Vista, and evidence that the new Windows 7 approach, while more pleasing to some, is inherently insecure.  He states, "This is dedicated to every ignorant ‘tech journalist’ who cried wolf about UAC in Windows Vista. A change to User Account Control (UAC) in Windows 7 (beta) to make it ‘less annoying’ inadvertently clears the path for a simple but ingenious override that renders UAC disabled without user interaction. For the security conscious, a workaround is also provided at the end. First and foremost, I want to clear up two things."

The flaw, which he calls "blatantly simple" to fix, was raised to his attention by a "security-minded 'whistleblower.'"  Ignored largely by Microsoft in chatter in its Windows 7 beta feedback, the issue may be present in the retail version of Windows 7 and has been known to many for some time.

Normally Windows 7 is set with the options "Notify me only when programs try to make changes to my computer" and "Don’t notify me when I make changes to Windows settings".  It uses a security certificate to determine if a program is part of Windows -- in other words, changes in the control panel don't raise warnings as they have a trusted certificate.

The "Achilles heel" as Mr. Zheng describes is that the UAC is a certified program and thus changes to it are also trusted -- even if that change is to disable it.  While he admits that he had to "think bad thoughts" to come up with a way of disabling the UAC without directly tricking the user into doing it, he says it wasn't tough.  He has posted a proof-of-concept VBScript, which uses keyboard shortcuts to select the UAC and then disable it.  The attack works against any user who has administrative permissions (as standard users are prompted for an administrative password when changing the UAC settings).

He elaborates, "We soon realized the implications are even worse than originally thought. You could automate a restart after UAC has been changed, add a program to the user’s startup folder and because UAC is now off, run with full administrative privileges ready to wreak havoc."

He adds, "This is the part where one would usually demand a large sum of money but since I’m feeling generous, there is a simple fix to this problem Microsoft can implement without sacrificing any of the benefits the new UAC model provides."

The fix, he says is to force the UAC into a secure desktop mode, whenever the UAC is changed, regardless of its state.  This, he says, while by no means foolproof, will prevent basic attempts.  He suggests Microsoft adopt the fix as soon as possible.

Microsoft, however, appears to be relaxed about the topic, as it responded to Mr. Zheng that the flaw is "by design", indicating it will not be changed before release.  Furthermore, as of this morning it has pulled a MSDN post about the topic which Mr. Zheng linked. 

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RE: ?
By BansheeX on 2/3/2009 5:39:40 AM , Rating: 2
You have no idea what you're talking about. None of your fevered ranting or poor analogies accomplishes anything. UAC prompts don't protect you from machine-compromising exploits, user privilege restrictions do. All a prompt does is ask someone twice whether they want to do what they intended. It's the user's access restrictions that causes malevolent code be impotent.

Mac has miniscule market share, of course it's safer. It's design isn't a factor yet, too few people are using it for hackers to care.

Dude, without some basic tools from software providers most of us idiots would be swimming in viruses.

Can Vista fanboys read? I am attacking the UAC prompts. UAC prompts. UAC prompts. Not antivirus software.

I expect it to be safe because ethical people are supposedly at the helm, making sure of it. What do you believe? I believe, protect 100% of users, that includes protecting grandparents, protecting teenagers, protecting businesspeople... everyone.

There is no such thing as 100% security, software can't address the latest worms and viruses the second they come out. If you actually believe that or try to convince others of that, you are proving my point. You can't just install some software and proceed to browse and e-mail with reckless abandon, you're going to learn a very hard lesson. People MUST educate themselves with the fundamentals, there is no magic shield you can buy to avoid that.

RE: ?
By anotherdude on 2/3/2009 1:38:21 PM , Rating: 2
UAC prompts don't protect you from machine-compromising exploits, user privilege restrictions do. All a prompt does is ask someone twice whether they want to do what they intended. It's the user's access restrictions that causes malevolent code be impotent.

Not sure what you are driving at here. UAC puts the entire machine into user mode which stops both the user and ANY RUNNING SOFTWARE from changing important OS files or settings without the user giving explicit assent.

Yes, this is no where near as safe as locking a machine down in user mode but doing that is impractical for many situations. Yes, if the user foolishly clicks through a UAC prompt without stopping to think it will not help but if the user is not even installing software or making system changes and a prompt comes up they should have the sense to say no, or can be trained to say no - part of "learning the fundamentals" as you say. It's not perfect but it helps.

"Spreading the rumors, it's very easy because the people who write about Apple want that story, and you can claim its credible because you spoke to someone at Apple." -- Investment guru Jim Cramer
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