Microsoft: Word 2007 crashes are a feature, not a bug

None of the flaws revealed last week demonstrate a vulnerability in Office, Microsoft claims

The Word 2007 bugs pegged as security vulnerabilities by an Israeli researcher are nothing of the sort, Microsoft said Thursday. Instead, the application crashes reported as flaws are actually by design.

The researcher who posted details last week of the bugs reacted by offering screenshots of the Word crashes and wondering why Microsoft disputed his findings.

On Monday, Mati Aharoni of Offensive Security warned of three new flaws in Word 2007 on the Milw0rm and SecurityVulns.com security sites, and posted malformed Word documents as proof-of-concepts. Microsoft, however, seemed unconcerned.

Late Wednesday, a company spokeswoman repeated the company's earlier contention that the Microsoft Security Response Center's (MSRC) investigation, "found that none of these claims demonstrate a vulnerability in Microsoft's Word 2007 or any part of the Microsoft Office System."

When asked to clarify that statement, she acknowledged Microsoft won't classify the flaws as security problems. Rather, the behaviour of Word 2007 is a feature, not a bug. "In fact, the behaviour observed in Microsoft Word 2007 in this instance is a by-design behaviour that improves security and stability by exiting Microsoft Word when it has run out of options to try and reliably display a malformed Word document," the spokeswoman said.

She went on to suggest that it is no big deal if Word 2007 did crash under those circumstances, a scenario that could lead to the loss of any unsaved data. "The sample code in [Aharoni's] postings cause Microsoft Word to crash, and users can restart the application to resume normal operations."

The stance was not out of character for the MSRC, which in the past has separated bugs that allow code execution or rights elevation from those that result in a denial-of-service-style situation. Previously, it has refused to label some crash-inducing problems as vulnerabilities, or patch them outside of a service pack.

That's the same position taken by David LeBlanc, one of Microsoft's secure code gurus, and Michael Howard, the co-author of the just-released Writing Secure Code for Vista. "You may rightfully say that crashing is always bad, and having a server-class app background, I agree. Crashing means you made a mistake, bad programmer, no biscuit," said LeBlanc in an MSDN blog. "However, crashing may be the lesser of the evils in many places. The theory is that it is better to crash, at least with client apps, than it is to be running the bad guy's shell code."

Office 2007 uses this strategy, said LeBlanc, who, like the MSRC, objected to classifying a denial-of-service-like result as an attack. "I really take issue with those who would characterize a client-side crash as a denial of service," he said. "If you can crash my app so that I can't restart it, or have to reboot my system, well, okay, that's a DoS. If you blew up my app, and I just don't load that document again, big deal."

For his part, Aharoni was puzzled by media reports that claimed Microsoft contested the bugs themselves, not that the flaws weren't to be considered true vulnerabilities, and responded by posting screenshots of the Word 2007 crash. "I've recieved [sic] many mails from full disclosure members confirming the crash," he also said on his blog Thursday. "I fully hope that Microsoft will find the resources to figure this out."

The company said it will continue to investigate, in case earlier editions of the word processor, which don't include code that purposefully crashes the app, are found to vulnerable. "Our investigation into the possible impact of these claims on other versions of Microsoft Office is continuing," said the spokeswoman.

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Gregg Keizer

Computerworld
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