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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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In fact, fuzzing tools appear to be the source of the deluge of Office flaws.

Once considered a crutch for the lowest form of code hacker - the much-denigrated "script kiddie" - data-fuzzing tools have gained stature to now be considered an efficient way to find vulnerabilities, especially obscure ones.

Fuzzers automate the process of trying to break an application by sending it unexpected data. Given a set of rules for constructing a file or an online form, a fuzzer will create every conceivable variation. Increasingly, vulnerability researchers and hackers are turning to tools to automate the discovery of flaws. For example, Next-Generation Security Software, a U.K. based technology consultancy, used a homegrown data-fuzzing tool to find the recent flaw fixed by Microsoft in the way Excel handles LABEL record files.

"Fuzzing and understanding file formats is the way that a lot of people are progressing along," said Sherief Hammad, founding director of NGSSoftware. "It is pretty easily, programmatically, to build up a file with malformed input. Sometimes that is a better way to analyze program flaws."

In July, security researcher HD Moore promised to release a browser bug every day of the month, highlighting the utility of data-fuzzing tools, but also the threat to software companies and their customers of falling behind the attackers in using such tools.

"Just like Moore is putting out a bug a day, these guys are using fuzzing tools and producing a large number of bugs," ISC's Sachs said.

Between Moore's focus on Internet Explorer flaws and the automated search for Office flaws, Microsoft's programmers have their work cut out for them, and system administrators should expect more fixes for software flaws from Microsoft. NGSSoftware, at least, has found two more vulnerabilities and reported them to Microsoft. In addition, the latest targeted Trojan horse attack uses a vulnerability in PowerPoint that the software giant still has to fix.

Moreover, the flaws reported to date are only due to a limited amount of effort using fuzzers, TippingPoint's Dhamankar stressed. Researchers do not typically have access to the detailed information about file formats for Microsoft's Office, so their efforts to date have been limited.

"What you are seeing right now is just investigation into one part of the file format, and people have a lot more records to look at," TippingPoint's Dhamankar said.

This article originally appeared in Security Focus.

Copyright © 2006, SecurityFocus

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