Security Advisor

New Critical IE Zero-Day Flaw Found

The latest flaw to strike every version of Microsoft's Web browser has been seen to be in active use by attackers.

Microsoft released Security Advisory 2963983 on Sunday night that details a new zero-day Internet Explorer flaw that has been seen to be used in limited online attacks.

The vulnerability, which affects all versions of Microsoft's Web browser, has only been seen targeting Internet Explorer 9 through 11, according to security firm FireEye, which initially discovered and reported the flaw to Microsoft.

According to the security firm, the flaw uses both a use-after-free vulnerability and an Adobe Flash exploit to bypass Windows' Data Execution Prevention (DEP) and Address Space Layout Randomization (ASLR) security features. The flaw has been seen being initialized when a user clicks on a link on a malicious Web site and can result in a remote-code-execution (RCE) attack.

"The exploit page loads a Flash SWF file to manipulate the heap layout with the common technique heap feng shui," said FireEye in a blog post. "It allocates Flash vector objects to spray memory and cover address 0×18184000. Next, it allocates a vector object that contains a flash.Media.Sound() object, which it later corrupts to pivot control to its ROP chain."

Both Microsoft and FireEye are holding back from providing any more in-depth details on the flaw due to the active nature of the zero-day vulnerability.

As Microsoft continues to investigate the flaw and possibly work on a security fix that would either be released in an out-of-band patch or with its next monthly security update, scheduled for May 13, the company has detailed a few ways to keep your system protected.

One option is to deploy Microsoft's Enhanced Mitigation Experience Toolkit (EMET) 4.1, which has been updated to guard against this specific attack. Once deployed, it will automatically configure to protect all versions of Internet Explorer.

Another choice for users is to change Internet security zone settings to block ActiveX and Active Scripting, only allowing for trusted sites to allow for ActiveX (Microsoft notes that setting the security options to block ActiveX may cause some Web sites to not function correctly). Also, instead of blocking, users can choose to be prompted whenever ActiveX and Active Scripting tries to run, allowing users to choose it to run on only sites they trust.

For Internet Explorer 11 users, activating Enhanced Protected Mode (EPM) in the browser will protect against this flaw.

According to Tyler Reguly, manager of security research at Tripwire, the most ideal action for enterprises to guard against attack is to go the EMET route. "The best advice is to ensure all systems have EMET deployed and that unnecessary browser add-ons are disabled," said Reguly in an e-mailed statement. "This should be part of an enterprises standard security posture and shouldn't require extra cycles or last minute deployment."

As a reminder, if and when an official Microsoft fix is released, those still running Windows XP machines will not receive the fix due to official security support ending for the aged OS earlier this month.

About the Author

Chris Paoli is the site producer for and


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