Apple QuickTime before 7.5 uses the url.dll!FileProtocolHandler handler for unrecognized URIs in qt:next attributes within SMIL text in video files, which sends these URIs to explorer.exe and thereby allows remote attackers to execute arbitrary programs, as originally demonstrated by crafted file: URLs.
The product receives input or data, but it does not validate or incorrectly validates that the input has the properties that are required to process the data safely and correctly.