Blogger: Windows 7 UAC feature still vulnerable

Citing a Microsoft document, he said the company won't fix UAC, which has a flaw that allows a remote user to take over a PC

The Microsoft blogger who first called attention to a security vulnerability in Windows 7's User Account Control (UAC) feature claims it still exists and that Microsoft won't fix it, even as the company nears final code completion on the OS.

Long Zheng, who writes the popular "I Started Something" blog, has posted a video online showing how UAC, a security feature first introduced in Windows Vista that sets user privileges on a PC in Windows 7, can be exploited.

Zheng also pointed to an instructional document by Microsoft Technical Fellow Mark Russinovich that attempts to explain UAC, saying it clearly states that Microsoft has no intention of fixing a change it made in the UAC in Windows 7 that leaves the new OS less secure because it allows someone to remotely turn the feature off without the user knowing.

Zheng first pointed out this change and its vulnerability back in February. At the time he said that the new UAC "standard user" default setting, which does not notify a user when changes are made to Windows settings, is where the security risk lies.

A change to UAC is seen as a change to a Windows setting, so a user will not be notified if UAC is disabled, which Zheng said he was able to do remotely with some keyboard shortcuts and code.

UAC has been a controversial feature since Microsoft introduced it in Windows Vista to improve its security and give people who are the primary users of a PC more control over its applications and settings. The features prevents users without administrative privileges from making unauthorized changes to a system.

In Russinovich's document, he does acknowledge that Zheng and others' observations about how third-party software can use the feature to gain administrative rights to a PC is accurate.

However, according to Zheng's blog post, Russinovich seemed to dismiss this possibility for remote code execution and offer no fix for it, because he said that there are other ways for malware to get into the system via UAC prompts.

"The follow-up observation is that malware could gain administrative rights using the same techniques," Russinovich wrote. "Again, this is true, but as I pointed out earlier, malware can compromise the system via prompted elevations as well.

From the perspective of malware, Windows 7's default mode is no more or less secure than the Always Notify mode ("Vista mode"), and malware that assumes administrative rights will still break when run in Windows 7's default mode."

Microsoft did not officially respond to a request for comment on Zheng's claim and video post. However, a company spokesperson said privately that Zheng may have misinterpreted Russinovich's document.

"The point seems to me to make it harder for malware to get on the system in the first place, by helping the end user make better decisions through the prompts they get, and having more and more users run in standard user mode vs. in admin mode (because admin mode is what exposes your machine to risks)," said the spokesperson, who asked not to be named, via e-mail.

Microsoft had stood by the change to UAC's default setting when Zheng made his first vulnerability claim, saying that the feature cannot be exploited unless there is already malicious code running on the machine and "something else has already been breached."

Microsoft has said that Windows 7, currently in a preview release, will be available to both businesses and consumers on Oct. 22. The release to manufacturing of the OS, at which all code will be final, is expected late next month.

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