Researcher sidesteps Microsoft fix for IE zero-day

Microsoft's short-term fix cannot cover all the different paths a criminal can take to exploit the bug, which the exploit highlights

A researcher has bypassed Microsoft's temporary fix for a zero-day Internet Explorer browser vulnerability that hackers have been exploiting for a month.

The exploit, developed by Peter Vreugdenhil of the vulnerability analysis company Exodus Intelligence, places pressure on Microsoft to release a permanent fix sooner rather than later. The software maker did not include a permanent patch in its advanced notification of seven security updates set for release next week. 

Vreugdenhil was able to bypass Microsoft's "fix it" in a fully patched Windows XP system running IE 8, said Brandon Edwards, vice president of Intelligence at Exodus. Microsoft released the temporary fix last week for the bug that affects IE6, IE7 and IE8 browsers released between 2006 and 2009.

Hackers started exploiting the flaw on Dec. 7 by planting malware on the respective servers running the websites of the Council on Foreign Relations, a foreign policy think-tank, and Capstone Turbine, a U.S. manufacturer of gas-powered micro-turbines. People visiting the sites with the affected browsers were open to having their computers hijacked and personal data stolen.

Vreugdenhil, an IE expert, was able to find a way around Microsoft's fix in six hours. "It's a quick turnaround time to identify a flaw in a fix," Edwards said.

Microsoft's temporary fix is meant to block the way the flawed code is being exploited in the wild by crashing the browser before malware can be installed. However, the fix cannot cover all the different paths a criminal can take to exploit the bug.

"What we did was identify another path to reach the vulnerability and exploit it," Edwards said. A permanent patch would involve rewriting the code, so the vulnerability no longer exists.

[See related: 10 ways to secure browsing in the enterprise]

Microsoft confirmed that Exodus had contacted it about the findings. "We are aware of this claim and have reached out to the group for more information," said Dustin Childs, group manager for Microsoft Trustworthy Computing.

While agreeing that Exodus' work added pressure on Microsoft to release a permanent fix, security experts said the company's Enhanced Mitigation Experience Toolkit would prevent criminals from exploiting the vulnerability. EMET is a utility Microsoft provides at no charge. The mitigation technology acts as a wall hackers must climb in order to reach a flaw.

"Organizations wanting safety until the official patch is released should be using EMET, as it is far superior to the one-click 'fix it," said Chester Wisniewski, a senior security adviser for Sophos.

In related news, Symantec linked the latest vulnerability to a sophisticated hacker group that the vendor calls the Elderwood gang. An analysis of the attack code used in the compromised Web sites revealed similarities to other code used by the group.

Since 2009, the group has used as many as nine zero-day exploits distributed in malware sent through targeted emails, known as spear phishing, or planted in hacked sites.

Zero-day vulnerabilities are especially valuable to cybercriminals because they affect software vendors have not yet patched flaws for.

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