New exploits discovered in the Angler Exploit Kit crimeware can bypass Microsoft’s vaunted Enhanced Mitigation Experience Toolkit (EMET) and then drop ransomware.
The finding by FireEye is the first time that EMET, Microsoft’s free tool that prevents malware from running on a Windows machine, has been unable to catch real malware. Researchers have hacked at EMET over the years looking for weaknesses—with some success--but until now there had been no real signs of bad guys abusing it.
The new exploits utilize vulnerable versions of the Adobe Flash and Microsoft Silverlight running on Windows 7, so keeping those application up-do-date with patches will prevent attacks on systems with EMET 5.5, the latest version of Microsoft’s tool. EMET is often relied upon to thwart zero-day attacks until patches get rolled out in organizations, so the new Angler feature would render that defense useless, according to FireEye.
“Nobody foresaw this coming,” says Raghav Pande, a research scientist with FireEye. Pande, who works on FireEye product security, says Angler and other malware typically look for EMET and if they find it, shut down and give up on an EMET-protected target. But this new variant “completely changed the dynamic” because it is able to bypass EMET detection, he says.
Microsoft, meanwhile, said this via a spokesperson: “EMET is designed to make it more difficult, expensive, and time-consuming, and therefore less likely, for attackers to exploit a system. With no one tool capable of preventing all attacks, Microsoft’s free security software detects and helps remove malware, including Angler.”
But the new EMET-bypass features in Angler demonstrate a growing sophistication of the malware kit’s developers as as well as their ability to target more security-savvy organizations: EMET is an open-source tool used as an extra layer by more advanced security teams.
“EMET is a great tool great tool to provide additional security to a system. Base security should be patching, which will neuter the attack in an even earlier stage. I have to say I am very impressed with the Angler engineering team: earlier this year, the 0-days, [and] now EMET bypass. This means they are targeting well-run organizations,” says Wolfgang Kandek, CTO of Qualys.
FireEye’s Pande says FireEye first spotted code in Angler for bypassing EMET back in March, but it’s now officially operational. The researchers didn’t witness any actual attacks, but were able to test the malware.
Bromium Labs in 2014 demonstrated how it could bypass several key defenses in EMET 4.1, specifically cheating EMET’s stack pivot protection and Export Address Table Filtering features by disabling them. Microsoft later that week released EMET 5.0, which hardened EAF and added Attack Surface Reduction, where organizations can selectively enable Flash, Java, and other third-party plugins.
Angler doesn’t use ROP to evade Data Execution Prevention; instead, it exploits Flash and Silverlight flaws.
In FireEye’s test of the malware, it saw that the exploit shellcode runs TeslaCrypt ransomware when infecting files. And “the attacker has full control over shellcode and it can pretty much execute anything it wants without EMET doing anything,” FireEye said in a new blog post with technical details and screenshots of the new Angler feature in action on Windows 7.
Pande says it’s possible the attack will work on Windows 8 machines as well, but FireEye has only tested Windows 7. Windows 10 would be immune due to the operating system’s ability to control app installation, he says.
Meanwhile, the new Angler features demonstrate just how far its creators have come. “If you compare past years’ attacks," Angler was rebundling exploits, Pande says. "It seemed they didn’t have the guys to tinker or play around with the exploit that much ... Right now, we’re seeing a change in the internal code and structure” of Angler, however, he says.
Patching Flash, Web browsers, and Java, can mitigate the EMET bypass, as can disabling Flash and Silverlight browser plug-ins, according to FireEye.
Michael Gorelik, vice president of R&D at Morphisec, says the Angler attack basically makes half of Windows users "defenseless" to ransomware. "The Angler Exploit Kit is already the preferred weapon of hackers to deliver their malware, and we predict that with this vulnerability, the prominence of Angler will further increase. This time the payload was TeslaCrypt Ransomware, but there is no limitation to what payload can be delivered," he says.
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