Internet Explorer Zero-Day Accidentally Leaked To Chinese Hackers

Outsmart Malicious Hackers

First up, happy new year – let’s hope 2011 is an interesting year for the infosec community. Anyway today’s story is about the recently released tool cross_fuzz by Michal Zalewski and an inadvertent leak that have occurred.

tl;dr version is something like this: Michal Zalewski writes a DOM fuzzer, fuzzes IE, finds flaws, Chinese dudes Google some .dll functions and find fuzzer results.

It could be some kind of weird coincidence, or you could read a whole conspiracy theory into it (unreleased tool, very specific search terms etc.).

Details concerning a potentially serious security vulnerability in fully patched versions of Microsoft’s Internet Explorer have been leaked to people in China, a researcher warned over the weekend.

Michal Zalewski, a security researcher at Google, blogged that data concerning at least one “clearly exploitable crash” in the Microsoft browser was inadvertently disclosed to people who were using a Chinese IP address. Details about the bug, which resides in the mshtml.dll component, were stored on a server that had accidentally been indexed by Google, Zalewski wrote elsewhere. On December 30, detailed search queries showed that the sensitive information, in addition to files for an unpublished security tool, had been retrieved by the unknown party.

“This pattern is very strongly indicative of an independent discovery of the same fault condition in MSIE by unrelated means,” Zalewski wrote. “Other explanations for this pair of consecutive searches seem extremely unlikely.”

The bug leads to arbitrary crashes in the EIP, or extended instruction pointer, of machines running the Microsoft browser. Zalewski said the flaw “is pretty much fully attacker-controlled.” It was uncovered using cross_fuzz, a security tool the researcher developed in his spare time more than two years ago to identify potential security vulnerabilities in IE, Firefox, and other browsers. Since its release, the tool has helped to identify nearly 100 various browser bugs.

You can find the complete history between MZ and Microsoft regarding both ref_fuzz and cross_fuzz here:


As for the ‘discovery’ it does seem likely that someone else had already discovered the same vulnerability and were searching for further information about it and if it had been published/disclosed. The search logs are here:


A statement attributed to Jerry Bryant, group manager in Microsoft’s Response Communications, said company researchers are working to reproduce the crash to see if the underlying vulnerability can be exploited by malicious hackers.

“At this point, we’re not aware of any exploits or attacks for the reported issue and are continuing to investigate and monitor the threat environment for any changes,” Bryant said.

Zalewski provided this account of his communications with Microsoft, which started in May 2008. In it, he claims that on December 21, Microsoft researcher David Ross “confirms being able to reproduce crashes locally right away.”

Zalewski said that Microsoft researchers asked him to delay the release of cross_fuzz until they had more time to investigate the crashes. He published his warning on New Year’s Day, after he learned that the crash logs and related files had been downloaded.

“These search queries are looking for information on two MSHTML.DLL functions – BreakAASpecial and BreakCircularMemoryReferences – that are unique to the stack signature of this vulnerability, and had *absolutely* no other mentions on the internet at that time,” he said.

cross_fuzz has been released officially now by Zalewski after Microsoft have had some time to investigate the crashes further. The moral of the story is, once again don’t use Internet Explorer!

As right now, there is a potentially dangerous 0-day for IE in the wild and as we well known with Patch Tuesday it’ll be quite some time before it gets fixed.

Source: The Register

Posted in: Exploits/Vulnerabilities, Windows Hacking

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