User interaction is required in that a target must open a malicious media file or visit a malicious page.
The specific flaw exists within the parsing of H.263 media files. The code within QuickTime trusts various values from MDAT structures and uses them during operations on heap memory. By crafting specific values the corruption can be leveraged to execute remote code under the context of the user running the application.
Patch Availability:
Apple has issued an update to correct this vulnerability. More details can be found at: http://support.apple.com/kb/HT4104