The specific flaw exists within the application's implementation of a custom compression algorithm. The application will trust a field within a DirectBitsRect structure which is used for an allocation, and later attempt to decompress data into this buffer. Due to the value for the allocation being different from the length of the data being decompressed a buffer overflow will occur which can lead to code execution with the privileges 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/HT4447