The sdp_parse_fmtp_config_h264 function in libavformat/rtpdec_h264.c in FFmpeg before 3.3.4 mishandles empty sprop-parameter-sets values, which allows remote attackers to cause a denial of service (heap buffer overflow) or possibly have unspecified other impact via a crafted sdp file.
https://lists.debian.org/debian-lts-announce/2019/01/msg00006.html
https://github.com/FFmpeg/FFmpeg/commit/c42a1388a6d1bfd8001bf6a4241d8ca27e49326d