This vulnerability allows remote attackers to execute arbitrary code on vulnerable installations of Apple Quicktime. 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 Quicktime handles the PnSize PICT opcode. It converts an unsigned 16 bit value into a signed 32 bit value. This value is later used as the size parameter for a memory copy function that copies from the file onto the stack. The results in a stack based buffer overflow that allows for remote code execution under the context of the current user.