The smka_decode_frame function in libavcodec/smacker.c in FFmpeg before 2.6.5, 2.7.x before 2.7.3, and 2.8.x through 2.8.2 does not verify that the data size is consistent with the number of channels, which allows remote attackers to cause a denial of service (out-of-bounds array access) or possibly have unspecified other impact via crafted Smacker data.
http://www.ubuntu.com/usn/USN-2944-1
http://www.debian.org/security/2017/dsa-4012
http://lists.opensuse.org/opensuse-updates/2015-12/msg00118.html
http://git.videolan.org/?p=ffmpeg.git%3Ba=commit%3Bh=4a9af07a49295e014b059c1ab624c40345af5892