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.
https://security.gentoo.org/glsa/201603-06
http://openwall.com/lists/oss-security/2013/12/08/3