The gif_decode_frame function in gifdec.c in libavcodec in FFmpeg before 1.2.1 does not properly manage the disposal methods of frames, which allows remote attackers to cause a denial of service (out-of-bounds array access and application crash) via crafted GIF data.
http://git.videolan.org/?p=ffmpeg.git%3Ba=commit%3Bh=d23b8462b5a4a9da78ed45c4a7a3b35d538df909
http://git.videolan.org/?p=ffmpeg.git%3Ba=commit%3Bh=7ee5e97c46e30fb3d6f9f78cc3313dbc06528b37