Flaw finders lay siege to Microsoft Office

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

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For most of the summer, Microsoft's Office product teams have had little time for development. Responding to a steady influx of flaws in the company's Office productivity suite has occupied many of Microsoft's programmers since late 2005. So far this year, the software giant has detailed at least 24 Office flaws found by outside researchers in its monthly bulletins, six times the number of Office flaws found in all of 2005. The count also surpasses the 20 flaws that Microsoft has fixed so far this year in Internet Explorer, a perennial favorite among vulnerability researchers.

The extraordinary jump in the number of flaws discovered by researchers in the components of Office has worried system administrators and forced Microsoft to spend development time on fixing the issues.

"When our security process gets activated, the application team is essentially ours," said Stephen Toulouse, security program manager for Microsoft's Security Response Center (MSRC). "It is not just that they are on-call, but they are working around the clock on response and updates."

The deluge of vulnerabilities for the Office programs - Word, Excel, PowerPoint, Outlook, and, for professional users, Access -signals a shift in the focus of vulnerability research and underscores the impact of flaw-finding tools known as fuzzers. The vulnerabilities in Office also highlight the threat that such files, if remained unchecked, can pose to a corporate network. Not since the days of macro viruses and Melissa have Office files posed such a danger to computer security.

The focus on Office flaws is a microcosm of the overall shift among vulnerability researchers from network service and server flaws to the application flaws that can be exploited to compromise a user's PC. Browsers, of course, are a popular target, but vulnerabilities have also been found in music-player software, image formats, the Macromedia Flash and Shockwave, e-mail readers and desktop security software.

"Nobody, I think, a year and a half ago would have thought that iTunes would have been a threat," Microsoft's Toulouse said.

Microsoft frequently sees such shifts in what vulnerability researchers find interesting, according to Toulouse. Yet, finding out what attracts researchers is more difficult, he said.

The initial signs of interest in Microsoft Office appeared last December, when one researcher attempted to auction off a vulnerability in Excel, only to have the high-profile auction canceled by eBay. Microsoft released its first major round of fixes for Office about four months later, approximately the average time that the software giant takes to patch flaws.

After that, a trickle turned into a flood.

"It's like someone opened the door and everyone wants to be in the same room," said Rohit Dhamankar, manager of security research for TippingPoint, a division of 3Com. "Once someone says, 'Look, this is an avenue of attack,' people from all over the world start concentrating on it."

TippingPoint, through its Zero-Day Initiative, has notified Microsoft of at least two flaws in Office discovered by independent researchers and patched by the software giant this year. TippingPoint's ZDI pays researchers a bounty for finding software flaws in common applications, a program that has caused some controversy.

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