Researchers Bypass Protections In Microsoft's EMET Security Tool

RSA CONFERENCE 2014 -- San Francisco -- Microsoft's free Enhanced Mitigation Experience Toolkit (EMET) 4.1 aimed at mitigating zero-day exploits can be cheated by attackers to sneak malware past it, researchers have found.

Bromium Labs, led by security researcher Jared DeMott, was able to successfully bypass several key defenses in Microsoft's EMET, mainly taking advantage of the inherent weakness of its reliance on known vectors of return-oriented programming (ROP) exploitation attack methods. "Any tool trying to block or prevent an exploit based on something that's known is always going to have that problem as an architecture," says Rahul Kashyap, chief security architect and head of security research at Bromium.

"There will always be some code you don't know about, like we demonstrate" in our research, says Kashyap, who is also the founder of Bromium. Bromium was able to bypass EMET's stack pivot protection and EAF (Export Address Table Filtering), which the researchers disabled.

Even so, the Bromium team says it would take a determined attacker building customized payloads to cheat EMET as they were able to do in their research. "EMET is a great tool; I would recommend it to people. It takes a lot of effort to be able to bypass everything available in it," Kashyap says. "We were able to craft an exploit to bypass EMET."

And there may even be more weaknesses in the tool, he says, if the researchers had dug "even deeper."

EMET's goal is to raise the bar and cost of exploitation for the attackers: "So the question really is not can EMET be bypassed. Rather, does EMET sufficiently raise the cost of exploitation? The answer to that is likely dependent upon the value of the data being protected. For organizations with data of significant value, we submit that EMET does not sufficiently stop customized exploits," Mott wrote in his paper.

Bromium alerted Microsoft with details of its research and recommended that EMET set virtual memory protection by default, come up with a new EAF protection approach, and expand return-oriented programming mitigations to 64-bit code. Kashyap says he expects Microsoft to address the issues in the next version of EMET.

Jonathan Ness, principal security development manager for Microsoft Trustworthy Computing, said EMET 4.1 has a setting that can prevent such bypasses. "Microsoft collaborated with Bromium on their latest research to ensure continued protection for our customers. The Enhanced Mitigation Experience Toolkit (EMET) 4.1 contains a setting to address this issue and help customers with their ongoing defense-in-depth strategies," he says.

Meanwhile, Mott says that even with the fixes Bromium recommends in its report for EMET, cheating the tool still could occur.

"But even with those fixes, many of the weaknesses are generic in nature and unlikely to be sufficiently addressed by userland protection technologies like EMET. EMET does not protect against kernel vulnerabilities, or help against non-exploit attacks such as Java sandbox escapes. Other similar technologies like Anti-Exploit and Core Force suffer from the same generic problem: mitigations that run on an even playing field with malicious code will/can be bypassed given sufficient attacker interest," Mott wrote in his report, which was published today. "To counter such attacks, we believe that an approach that does not rely on exploitation payload based vectors is needed. As demonstrated, exploit payloads continue to evolve."

[One of the three finalist entries for Microsoft's first-ever BlueHat Prize for building new security defense technologies is now part of the software giant's free Enhanced Mitigation Experience Toolkit (EMET). See Microsoft Adds BlueHat Prize Finalist's Technology To Its Free Toolkit .]

This isn't the first time researchers have been able to sneak malware past EMET: Three other researches previously demonstrated bypasses of earlier versions of the tool. Mott presented his findings here today at the B Sides conference. His paper is available for download via this link.

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