Researcher reveals how IE flaw can turn your PC into a public file server

In a live demonstration Wednesday at the Black Hat DC conference, a security consultant showed how it's possible to exploit a flaw in the Microsoft Internet Explorer browser to remotely read files on the victim's local drive, prompting a security advisory from Microsoft.

The flaw, said to extend across all versions of Internet Explorer, is not subject to a patching fix, according to Jorge Luis Alvarez Medina, the Argentina-based security consultant with Core Security Technologies who elaborated on the attack technique during his demo. Indeed, Microsoft advised anyone concerned about the potential for this type of attack to run IE in "protected mode", a workaround that Medina also advised.

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Other workarounds in IE, according to Medina, would include setting "IE Network Protocol Lockdown," adjusting the security level setting for the Internet and Intranet Zones to "high," and disabling Active Scripting for the Internet and Intranet Zones with a custom setting.

But he also noted that since this attack appears to only work against IE, users might want to consider using "a different browser to navigate untrusted Web sites". Medina said it doesn't appear that the IE flaw is subject to patching because it encompasses design features related to how IE and Windows Explorer handle zone elevation, HTML code and MIME types. There are a few ways to instigate the attack, which is somewhat complex because you have to "string all of these features together to build an attack tool," Medina said. One method involves enticing the victim to click a link to a malicious Web site.

One weakness in IE is that it "doesn't behave consistently… when accessing the same resources," he pointed out. The exploit demonstrated by Medina basically involves "chaining the exploitation of a series of weak features." He said the dialog with Microsoft's security team about the exploit so far has indicated that Microsoft thinks this is not something it can fix because the flaw is so much a part of the fundamental design of the browser.

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