Microsoft is warning that a previously disclosed flaw in Apple's Safari browser could have dire consequences for Windows users.

The Safari bug, originally disclosed on May 15 by security researcher Nitesh Dhanjani, allows attackers to litter a victim's desktop with executable files, an attack known as "carpet bombing."

It turns out that if this flaw is exploited in combination with a second unpatched bug in Internet Explorer, attackers can run unauthorized software on a victim's computer, according to Aviv Raff, a security researcher. Raff says he originally reported the IE flaw to Microsoft more than a year ago, and then told them about how it could be combined with the carpet bombing bug just over a week ago.

IDG Applications Service tested Raff's demonstration attack code, which runs Windows Calculator on a victim's system. For the attack to work, a victim must first visit a maliciously crafted Web page with the Safari browser, which in turn will trigger the carpet bombing attack and exploit the IE flaw.

Both the Safari and IE bugs "are moderate vulnerabilities that, combined, produce a critical flaw, which allows remote code execution," Raff said in an instant message interview.

Microsoft is taking the issue seriously. It released a security advisory on the problem late Friday, a sign that it may be working on a patch for the IE flaw. The advisory says that the vulnerability has to do with the way Windows handles desktop executables and recommends that Windows users "restrict use of Safari as a web browser until an appropriate update is available from Microsoft and/or Apple."

The attack reportedly affects all versions of Windows XP and Vista, Microsoft said.

Apple may not be rushing out to patch this bug, however. Dhanjani says that Apple has told him that it is not treating the Safari bug as a security issue, a response that has generated criticism from the security community. Last week, for example, the consumer advocacy group Stopbadaware.org urged Apple to reconsider this stance.

According to Raff, unless Apple patches the bug, more attacks like the one he found in IE are likely to pop up. "This is not the only issue that can be combined with the Safari vulnerability," he said. "If Microsoft fixes this, Safari users will still be vulnerable."

Apple didn't immediately respond to a request for comment.