Microsoft IE Zero-Day Flaw Exposure Widens

By Sean Michael Kerner  |  Posted 2013-10-02

Microsoft IE Zero-Day Flaw Exposure Widens

Two weeks ago, Microsoft first warned its users that it was investigating public reports about a zero-day vulnerability in its Internet Explorer (IE) Web browser. It's a vulnerability that still has not been patched in a full update and is now actively being exploited by attackers.

In response to an inquiry from eWEEK about the issue, Microsoft declined to provide any specific timing about when a full patch for the issue, now known as CVE-2013-3893, would be available.

"We are aware of a limited number of targeted attacks; customers who have installed the Fix It are not at risk from this issue," a Microsoft spokesperson said. "We encourage customers who have not applied the Fix It provided by Security Advisory 2887505 to do so to help ensure they are protected as we continue work on a security update."

The Fix It is a "Band-Aid" approach to the security issue, providing a fix for users who physically visit the Fix It site and click the Fix It button. A full patch, in contrast, is made available to all Microsoft users through the Windows Update mechanism that all Windows users have access to and many users have set for fully automated patching.

Ken Pickering, director of engineering at CORE Security, told eWEEK that there are already at least four advanced persistent threats (APTs) known to be using the CVE-2013-3893 attack as part of their spearphishing campaigns on prospective targets. Spearphishing is a form of targeted fake email (phishing) attack. The fact that the vulnerability is being actively exploited should merit an emergency response from Microsoft, Pickering added.

"Realistically, people should avoid using IE if possible until the patch for this fix is released," he suggested.

Adding further fuel to the fire is the fact that the CVE-2013-3893 vulnerability has now been weaponized inside of the open-source Metasploit penetration testing framework. Metasploit is a popular tool used by security researchers to conduct security analysis. Security researchers have been landing Microsoft zero-day flaws in Metasploit as they pop up since at least 2005.

The fact that CVE-2013-3893 is now in Metasploit compounds the impact of the issue, according to Pickering.

"I personally believe in responsible release of exploits, giving the vendor time to appropriately patch the problem rather than making the situation even worse by giving unskilled attackers the capability to abuse this zero-day," Pickering said. "Even in this case where the exploit is publicly disclosed, including it in any framework before Microsoft has had a chance to roll something out can potentially make the situation much worse."

Microsoft IE Zero-Day Flaw Exposure Widens

Tyler Reguly, technical manager of security research and development for security vendor Tripwire, told eWEEK that there are two sides to releasing an exploit.

"It puts the exploit in the hands of malicious users, but it also allows pen testers to audit enterprises to discover systems and users that may not have switched from IE to another browser," Reguly said.


Reguly noted that he had originally expected an out-of-band patch for the CVE-2013-3893 issue. Microsoft issues regular updates on the second Tuesday of every month. The next Patch Tuesday is set for Oct. 8, and as such Reguly does not expect Microsoft to put out an emergency patch before then.

Darien Kindlund, manager of threat intelligence for FireEye, told eWEEK that patching this issue is nontrivial.  

"The exploit affects all major versions of IE; therefore, Microsoft may require additional time to construct a proper patch covering all of these versions," he said.

Consumers have used the Fix It tool, and it seems to work for them, Kindlund noted.

"Enterprises have not adopted the tool for widespread use, largely because it is not as maintainable as a formal hotfix," Kindlund said.

With a formal hotfix patch, existing enterprise patch management systems can be used to deploy and manage system patching.

Rather than the Fix It, Kindlund suggests that enterprises deploy and use the Enhanced Mitigation Experience Toolkit (EMET). EMET is a free tool for Windows users that provides security risk mitigation capabilities. According to Kindlund, EMET correctly addresses and mitigates not only this recent exploit, but previous zero-days as well.

"To be honest, we are surprised that Microsoft has not made EMET mandatory on their Windows platform, as it is a tool that is available now which would have prevented this widespread compromise, to begin with, he said.

Sean Michael Kerner is a senior editor at eWEEK and Follow him on Twitter @TechJournalist.

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