Firefox update slams door on IE zero-day bug

Mozilla late yesterday patched Firefox to fix nine bugs, including the controversial critical vulnerability that involved both the open source Web browser and Microsoft's Internet Explorer.

Firefox 2.0.0.5, which can be downloaded in versions for Windows, Mac OS X, and Linux in 42 localized editions, fixes the "firefoxurl://" vulnerability that can be exploited only on systems where Firefox is installed but IE is the primary browser. For the past week, researchers have quarreled over whether Mozilla or Microsoft was responsible for the flaw and which company should patch its software.

In the security advisory, one of eight issued yesterday that outline the nine bugs, Mozilla again refrained from expressly putting the onus on Microsoft. But as before, it came close.

"Other Windows applications can be called in this way and also manipulated to execute malicious code," read the advisory. "This fix only prevents Firefox and Thunderbird from accepting bad data. This patch does not fix the vulnerability in Internet Explorer."

And more blunt was the single suggested work-around. "Mozilla highly recommends using Firefox to browse the Web to prevent attackers from exploiting this problem in Internet Explorer," it said.

One of the researchers who last week pinned blame on Microsoft had not changed his tune as of yesterday. "This [Firefox patch] does not actually fix the flaw in Internet Explorer, but simply patches one of the myriads of attack vectors," said Thor Larholm, a Danish researcher who publicized the exploit. "I can definitely understand the initial reaction from Microsoft. Most of the emphasis in the public vulnerability reports were dealing with Firefox, the '-chrome' command-line argument, and how to properly escape the exploit code.

"However, I can still automatically launch a wide range of external applications from Internet Explorer and provide them with arbitrary command-line arguments, [including] AcroRd32.exe (Adobe Acrobat PDF Reader), aim.exe (AOL Instant Messenger), Outlook.exe, msimn.exe (Outlook Express), netmeeting.exe, HelpCtr.exe (Windows Help Center), mirc.exe, Skype.exe, wab.exe (Windows Address Book), and wmplayer.exe (Windows Media Player), just to name a few," Larholm wrote.

Microsoft's position last week has been that IE is not buggy and so wouldn't be patched. "Microsoft has thoroughly investigated the claim of a vulnerability in Internet Explorer and found that this is not a vulnerability in a Microsoft product," a spokesman said last Thursday.

Other patches put into place by 2.0.0.5 included multiple memory corruption bugs. "With enough effort ... some of these could be exploited to run arbitrary code," a cross-site scripting vulnerability and a flaw that could give attackers access to the browser's cache.

Mozilla picked up the pace to push Firefox 2.0.0.5 out to users earlier than scheduled. On Monday, Mozilla developers pegged the update as a "fire drill release" because of the critical nature of the firefoxurl:// bug. At the time, July 19 was the target for 2.0.0.5's release. "But we might be able to accelerate the release," notes from a weekly status meeting read.

This is the first update to Firefox since support for the older 1.5.x line was discontinued. Earlier this month, users of that version were offered an automatic update to Firefox 2.0.0.4.