Apple on Wednesday issued a security patch for its Safari Web browser that fixes a widely reported vulnerability and three other holes, two of which affect only Windows versions.

At the CanSecWest security conference last month, security researchers Charlie Miller, Jake Honoroff, and Mark Daniel, from Independent Security Evaluators, managed to compromise a MacBook Air using a zero-day vulnerability in Safari.

Tipping Point, the sponsor of the contest, said the vulnerability would not be disclosed until Apple issued a patch.

Among the four vulnerabilities fixed in Wednesday's Safari patch is CVE-2008-1026, which Apple thanked Miller for reporting.

Apple describes the flaw thus: "A heap buffer overflow exists in WebKit's handling of JavaScript regular expressions. The issue may be triggered via JavaScript when processing regular expressions with large, nested repetition counts. This may lead to an unexpected application termination or arbitrary code execution."

To fix the problem, Apple said it added validation to JavaScript regular expressions.

A second WebKit vulnerability was also addressed. WebKit is an open source engine used by Apple's Safari, Mail, and other applications. Both WebKit issues affect Mac and Windows users of Safari.

The other two vulnerabilities affect only Safari for Windows XP or Vista. One is a timing flaw that could allow a maliciously crafted Web page to spoof a legitimate site by changing the contents of Safari's address bar without loading the associated page. The other is a memory corruption issue that could allow for the remote execution of malware following an attempt to download a maliciously crafted file.

The Safari patch can be downloaded through the Mac OS X Software Update control panel, or from Apple's Web site.

Safari's share of the browser market remained relatively flat throughout 2007, at about 1.7%, according to W3Schools. It has become more popular, however, in 2008. In March, Safari had a 2.1% market share. Microsoft's various versions of Internet Explorer accounted for 53.1% of the visitors to the W3Schools site in March, while Firefox accounted for 37%.