Type confusion

MP4Atom::factory in mp4atom.cpp in MP4v2 2.0.0 incorrectly uses the MP4ItemAtom data type in a certain case where MP4DataAtom is required, which allows remote attackers to cause a denial of service (memory corruption) or possibly have unspecified other impact via a crafted MP4 file, because access to the data structure has different expectations about layout as a result of this type confusion.