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“Operation Clandestine Fox” Now Attacking Windows XP Using Recently Discovered IE Vulnerability

On April 26th, FireEye Research Labs notified the public of a new IE zero-day exploit being used in “Operation Clandestine Fox.” The initial attack targeted users of IE versions 9, 10, and 11 on Windows 7 and 8. Despite attackers only targeting those versions of Microsoft IE and Windows OS, the vulnerability actually impacts all versions of IE from 6 through 11.

Today, FireEye Labs can reveal a newly uncovered version of the attack that specifically targets out-of-life Windows XP machines running IE 8. This means that live attacks exploiting CVE-2014-1776 are now occurring against users of IE 8 through 11 and Windows XP, 7 and 8.

We have also observed that multiple, new threat actors are now using the exploit in attacks and have expanded the industries they are targeting. In addition to previously observed attacks against the Defense and Financial sectors, organization in the Government- and Energy-sector are now also facing attack.

Mitigation

In our tests, disabling VXG.dll blocks this attack on all configurations of IE and Windows OSs. However, we strongly suggest that Windows XP users upgrade to a later Windows operating system to take advantage of new mitigation technologies from Microsoft, such as EMET 5.0 and IE with Enhanced Protected Mode (EPM). Deploying preventative measures now will help mitigate the impact of these exploits until Microsoft patches the underlying vulnerability, and will offer additional protection from future ZeroDay exploits.

Details

The main differences between this new attack targeting Windows XP compared to the original Windows 7/8.1 versions of this attack are the mitigation bypasses. The Windows 7/8.1 version develops its write primitive into read/write access to much of the process space by corrupting Flash vector objects. This is to bypass ASLR by searching for ROP gadgets and building a ROP chain dynamically in memory.

Without ASLR, ROP gadgets can be constructed beforehand with static addresses. Consequently, Flash assistance in the Windows XP version is much simpler. It builds a ROP chain with static addresses to gadgets in MSVCRT, tweaks addresses for a plethora of language packs, and jumps directly to a pivot without developing a write primitive. From there, the ROP chain calls VirtualAlloc to allocate executable memory, copies the shellcode to the allocated chunk, and executes the shellcode.

This new tactic of specifically targeting those running Windows XP means the risk factors of this vulnerability are now even higher. We have been working with Microsoft and they have released an Out of Band patch. FireEye highly recommends users of Microsoft Internet Explorer apply the patch as soon as possible for security reasons.