Flaws galore in IE and Firefox

Equal-opportunity hacking


Polish security researcher Michal Zalewski, known for his seemingly unending stream of browser vulnerability discoveries, has struck again. This time he's reported four flaws that are sure to get the attention of bug squashers in both Microsoft and Mozilla camps.

The most serious vulnerability could make it possible for cyber crooks to steal sign-on cookies from online banks and other trusted sites and possibly execute attack code on a victim's machine. Zalewski's findings, which included a total of four vulnerabilities - for good measure, two for IE and two for Firefox - were reported earlier today on the Full Disclosure mailing list.

IE's cookie flaw, the only one of today's batch rated "critical," resides in the browser's "page update race condition." In essence, there is a brief window of opportunity when IE navigates from a sensitive web page to an unrelated site. During this time an attacker could execute javascript actions belonging to the old page that uses actual content supplied the newly loaded site. This opens up a host of harsh possibilities, including the reading or setting of cookies controlled by the trusted site, changing form submission URLs, injecting code or crashing the browser.

"In other words, the entire security model of the browser collapses like a house of cards and renders you vulnerable to a plethora of nasty attacks," Zalewski wrote on a page that demonstrates the vulnerability. "Local system compromise is not out of question, either."

A second IE flaw affects version 6 and allows for the mimicking of an arbitrary website, possibly including those delivering content over a protected SSL channel. The vulnerability, which Zalewski rated "medium," doesn't affect IE 7 because of high-level changes built into the browser.

A Microsoft spokesman says the company's security researchers are investigating the two reported flaws.

Proving to be an equal-opportunity identifier of security flaws, Zalewski also reported two vulnerabilities in Firefox. One of them, which the researcher rated "major," takes advantage of the way the open-source browser handles iframes to potentially allow an attacker to monitor a user's keystrokes or spoof content on a page the user is viewing. Somewhat mitigating any exploit, the vulnerability involves what's known as the document.write method to allow a third-party site to replace iframes on unrelated pages. That means direct interaction with the rest of an attacked site isn't possible.

The second Firefox vulnerability resides in the delay timers implemented during some confirmation dialogs. By initiating a sequence of blur/focus operations, an attacker could cause a victim to download and execute code. Zalewski rated the flaw "medium".

He has made a regular habit of sniffing out vulnerabilities in a wide range of applications (besides Firefox and IE, he's also poked holes in Sendmail) and that run on a variety of platforms, including Windows and Unix. His research underscores what should be a growing realization among security experts that nearly every piece of code can be misused and abused by a determined attacker. ®


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