By Robert Lemos, SecurityFocus
Published Thursday 13th April 2006 14:58 GMT

Last month, security researcher HD Moore decided to write a simple program that would mangle the code found in web pages and gauge the effect such data would have on the major browsers. The result: hundreds of crashes and the discovery of several dozen flaws.

The technique - called packet, or data, fuzzing - is frequently used to find flaws in network applications. Moore and others are now turning the tool on browsers to startling results. In a few weeks, the researcher had found hundreds of ways to crash Internet Explorer and, to a lesser extent, other browsers.

In another example, it took less than an hour at the CanSecWest Conference last week for Moore and computer-science student Matthew Murphy to hack together a simple program to test a browser's handling of cascading style sheets (CSS), finding another dozen or so ways to crash browsers.

"Fuzzing is probably the easiest way to find flaws, because you don't have to figure out how the application is dealing with input," said Moore, a well-known hacker and the co-founder of the Metasploit Project. "It lets me be a lazy vulnerability researcher."

Tracing the root causes of the crashes has resulted in the discovery of more than 50 flaws in Internet Explorer, a handful of which could be used to gain control of a website visitor's Windows system, Moore said. Other browsers had far fewer flaws, but each one had at least one remotely exploitable vulnerability that could be used to exploit users' systems, Moore said.

Microsoft stressed that the issues are still under investigation.

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