'Aurora' Exploit Retooled To Bypass Internet Explorer's DEP Security

Security experts' worst fears about the Internet Explorer exploit used to hack Google and others has been realized: It can be retooled to beat IE's best defense, the Data Execution Protection (DEP) feature.

Some researchers are actively working on ways to use the malicious code in the so-called "Aurora" attacks to bypass DEP, a security feature in Windows and available for IE that prevents so-called "heap-spray" style code execution by malware. And one group of researchers claims to have demonstrated that the exploit can bypass DEP: VUPEN Security says it has confirmed that DEP doesn't prevent the exploit and that the only way to stop it is to disable JavaScript.

Chaouki Bekrar, CETO of VUPEN Security, says his team was able to bypass DEP on IE8 and execute arbitrary code. "We first used this technique a few weeks ago when we exploited another IE8 vulnerability [that was] fixed with MS09-072," Bekrar says. He says VUPEN has sent its exploit code to Microsoft for review. IDS, IPS, and antivirus vendors also were given access to it via the company's vulnerability analysis service.

DEP is one of the key defenses against the original Aurora exploit code, which to date has been threatening only IE 6 users in the wild after being released in the wake of the recent hacks of Google and other firms.

Meanwhile, renowned researcher Dino Dai Zovi has written an Aurora exploit that works on IE 6 and IE 7 on XP, as well as IE 7 on Vista. His exploit works in IE browsers that don't have DEP enabled. "[But] the ASLR used in IE 7 for Vista does not prevent my exploit from working in that configuration," Dai Zovi says.

Dai Zovi says the Aurora exploit could be reworked to bypass DEP, too: "The Aurora exploit can be retooled to bypass DEP, including Permanent DEP on IE 8 and XP SP3," Dai Zovi says. But IE 8 with Address Space Layout Randomization (ASLR) and permanent DEP "is significantly more challenging," he says.

ASLR is basically a security feature in Vista that protects the system from an exploit attempting to call a system function. It places placing code in random areas of memory that makes it more difficult for an attacker to run malware on a machine.

"It is unclear whether it is a DEP bypass for DEP on XP SP2 or Permanent DEP on XP SP3, which requires more work to bypass," says Dai Zovi, who is co-author of The Mac Hacker's Handbook.

VUPEN's Bekrar confirmed that his firm's exploit bypasses "permanent DEP."

Dan Kaminsky, director of penetration testing for IOActive, said in an interview last week that the Aurora exploit could be retooled to bypass DEP. He reitered that today: "There is zero expectation that DEP, without ASLR, is impregnable. We know it isn't," he says. "There is some expectation that DEP with ASLR is something of a bar to pass, though."

A Microsoft spokesperson said the company is investigating the DEP bypass issue. "Once we're done investigating, we will take appropriate action to help protect customers. This may include providing a security update through the monthly release process, an out-of-cycle update or additional guidance to help customers protect themselves," the spokesperson says.

Meanwhile, Microsoft last night had issued an advisory saying it would issue an emergency patch for the IE flaw, and recommended that users upgrade to IE 8.

"We want to let customers know that we will release this security update as soon as the appropriate amount of testing has been completed. While we cannot yet give a date of when that will be, we will keep customers updated," said Jerry Bryant, senior security program manager for Microsoft, in the blog post.

In another development, Reuters reported that sources say Google is investigating the possibility that the attacks were done with the help of people working inside Google's China offices.

Meanwhile, France has joined Germany in telling its citizens to shelve IE for another browser until Microsoft patches the flaw -- a move that security researchers say is an overreaction to the situation.

"I think we're getting a mix of state pride and technical ignorance. Firefox development is an international affair, and there's a good couple of decades of inertia behind bashing Microsoft. But it's not like there has been any shortage of critical vulnerabilities found in Firefox -- I myself found three or four last year," IOActive's Kaminsky says. "Adobe Acrobat has had a rougher year than all the browsers combined, and if you remember, the widespread belief at the beginning of this affair was that another zero-day in the PDF was being exploited. I certainly didn't hear Germany and France arguing to abandon PDF."

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