User interaction is required to exploit this vulnerability in that the target must visit a malicious page or open a malicious file.
The specific flaw exists within how WebKit processes a range object as defined with the DOM level 2 specification. When processing the contents of a range, WebKit will fail to accommodate for manipulation of the DOM due to an event listener. This can lead to code execution under the context of the application.
Patch Availability:
Apple has issued an update to correct this vulnerability. More details can be found at: http://support.apple.com/kb/HT4554