An attacker who successfully exploits the vulnerability could perform a session fixation attack. This allows the attacker to pre-set the victim's session ID and to use the fixed session ID for malicious activities.
An attack of this sort, known as "cross-site cooking," might include tricking a user to log in through a malicious form, exploiting a cross-site scripting vulnerability or meta tag injection flaw, breaking into host in the target server's domain, and network traffic alteration.
Attacks making use of this vulnerability have not yet been reported. Apple has not yet addressed the flaw.
Apple's Safari browser has been singled out by Microsoft and other security researchers recently for security problems.
In late May, Microsoft said was investigating reports of "a blended threat that allows remote code execution on all supported versions of Windows XP and Windows Vista when Apple's Safari Web browser has been installed."
Last week, security researcher Aviv Raff said that Apple's iPhone Mail and Safari applications are vulnerable to URL spoofing.
In a blog post earlier this month, Raff said that Apple has not learned from past browser design mistakes.
With two days left in July, Apple's Safari browser market share stands at 6.31% worldwide, according to Net Applications. That's an increase of more than 37% from its 4.58% market share in July 2007.