The decode_slice_header function in libavcodec/h264.c in FFmpeg before 2.1 incorrectly relies on a certain droppable field, which allows remote attackers to cause a denial of service (deadlock) or possibly have unspecified other impact via crafted H.264 data.
http://openwall.com/lists/oss-security/2013/11/26/7
http://openwall.com/lists/oss-security/2013/12/08/3
https://github.com/FFmpeg/FFmpeg/commit/29ffeef5e73b8f41ff3a3f2242d356759c66f91f