The format_line function in log.c in libavutil in FFmpeg before 1.2.1 uses inapplicable offset data during a certain category calculation, which allows remote attackers to cause a denial of service (invalid pointer dereference and application crash) via crafted data that triggers a log message.
http://git.videolan.org/?p=ffmpeg.git%3Ba=commit%3Bh=cc0dd86580b3257f22a4981a79eb5fa6804182b6
http://git.videolan.org/?p=ffmpeg.git%3Ba=commit%3Bh=7edb984dd051b6919d7d8471c70499273f31b0fa