This vulnerability allows remote attackers to execute arbitrary code on vulnerable installations of Apple Safari. 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 the way Safari manages the lifetime of TextTrack objects. By manipulating a document's elements an attacker can force a dangling pointer to be reused after it has been freed. An attacker can leverage this vulnerability to execute arbitrary code under the context of the current process.