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Flaw finders lay siege to Microsoft Office

'These guys are using fuzzing tools and producing a large number of bugs'

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While a vulnerability in a remote network service could be exploited to create a worm and tends to worry system administrators more, the rash of attacks leveraging the Office vulnerabilities to compromise specific companies underscores the seriousness of the current threat.

A limited number of companies have been targeted by Trojan horse Word documents, Excel spreadsheets, and PowerPoint presentations containing code to exploit previously unknown flaws within Office. The attacks appear to continue a trend of targeted espionage coming from within China. While security experts are careful to point out that the attacks may just be entering the U.S. from a compromised Chinese server, the continuing attacks from the same IP address space increasingly make that unlikely.

Not only are the attacks coming from China, but Chinese hacker clubs appear to be showing the lion's share of interest in finding flaws in Office, according to security experts. These groups are focused on using flaw information for financial gain, said Marcus Sachs, director of the SANS Internet Storm Center and the deputy director of the computer science laboratory at SRI International.

"My conclusion is the source of most of this trouble is coming out of China," Sachs said. "I think the technicians who are finding the flaws are selling the method of access to the intelligence or espionage community."

The hacker groups appear to be using data-fuzzing techniques to find flaws in Excel and other Office applications, agreed David Cole, director for Symantec's Security Response group. (SecurityFocus is owned by Symantec.)

"Given the number of Office flaws, it really feels like someone is fuzzing Microsoft Office and creating malicious files with the results," Cole said. "Someone is adamant about finding this stuff."

Of the public flaws detailed by Microsoft in July, at least four appear to have come from Chinese researchers. Other flaws were found as part of a vulnerability bounty program, so the sources of those issues are unknown. In total, at least seven of the last seventeen flaws appear to come from efforts by Chinese researchers.

"This is reminiscent of a few years ago when Russian (researchers) were doing stuff using issues in IIS and browser helper objects," ISC's Sachs said.

While Office files require some user interaction to compromise a victim's system, most workers are now accustomed to receiving such files, especially if attached to an e-mail that appears to be genuine, said Mikko Hyppönen, chief research officer for antivirus firm F-Secure.

"First and foremost, it is the easiest way to get through the most obvious barriers to entry in a corporate network: the firewall and antivirus," Hyppönen said. "If you try to use other executable code, the firewall or antivirus software will stop you. It is much easier to get in to reach the desktop if the document you are sending is an Excel file or a PowerPoint file or a Word file."

Hyppönen expects the attacks to continue, driven by a readily available source of flaws generated by fuzzing tools.

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