Mozilla patches 11 Firefox bugs, six critical

Among the fixes is a plug for the SSL hole reported by Microsoft researchers

Mozilla on Thursday patched 11 vulnerabilities in Firefox, more than half of them labeled "critical."

The update was the first since late April, when Mozilla rushed out a refresh to plug a hole that the company's developers has inadvertently introduced in the Windows version of the browser, and came just days after the launching of a "tweener" build of the upcoming Firefox 3.5.

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Of the 11 flaws fixed in Firefox 3.0.11, six were rated critical, one "high," two "moderate" and two "low" in Mozilla's four-step system.

Three of the six critical bugs were in the browser's rendering and JavaScript engines, a frequent target of Mozilla's patching. "Some of these crashes showed evidence of memory corruption under certain circumstances and we presume that with enough effort at least some of these could be exploited to run arbitrary code," Mozilla said in the advisory for the engine patches, using its now-standard boilerplate language.

The SSL tampering vulnerability was reported to Mozilla by three researchers working for browser rival Microsoft, and a fourth at Purdue University. The four -- Shuo Chen, Ziqing Mao, Yi-Min Wang and Ming Zhang -- co-wrote a paper titled "Pretty-Bad-Proxy: An Overlooked Adversary in Browsers' HTTPS Deployments," that they published May 1 ( download PDF). Mozilla ranked the vulnerability as "high."

Other patches prevent hackers from pinching browser cookies, executing JavaScript attack code and spoofing Web addresses.

Thursday's update was the fifth this year for Firefox 3.x, but not the first for Mozilla's browsers this week.

On Monday, Mozilla rolled out Firefox 3.5 Preview, a build the company said is a near-finished version of the official Release Candidate, or RC. Although new-found bugs had delayed the RC's release yet again, Mozilla wanted to get something in testers' hands, and so took the unusual step of delivering the Preview.

At this point, Mozilla has not set a scheduled for posting Firefox 3.5 RC, once slated to appear the first week of June. In notes on a status meeting the company held Wednesday, Mozilla simply noted that it would release the RC "you know, when it's ready."

Firefox 3.5 Preview is being offered only to users who have already installed Beta 4 of the browser upgrade.

Firefox 3.0.11 can be downloaded for Windows, Mac OS X and Linux, but current users can also call up their browser's built-in updater or wait for the automatic update notification, which should pop up in the next 48 hours.