User interaction is required in that the user must coerced into visiting a website or opening a malicious document. The specific flaw exists within how the library removes a particular container element containing another element holding the contentEditable attribute. Upon removal of the container during a particular event, the library will traverse the tree and access the contentEditable element that was freed. 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/HT4196