The oggplay_data_handle_theora_frame function in media/liboggplay/src/liboggplay/oggplay_data.c in liboggplay, as used in Mozilla Firefox 3.5.x before 3.5.4, attempts to reuse an earlier frame data structure upon encountering a decoding error for the first frame, which allows remote attackers to cause a denial of service (NULL pointer dereference and application crash) or possibly execute arbitrary code via a crafted .ogg video file.