libavcodec/gifdec.c in FFmpeg before 2.4.2 does not properly compute image heights, which allows remote attackers to cause a denial of service (out-of-bounds access) or possibly have unspecified other impact via crafted GIF data.
The product performs operations on a memory buffer, but it reads from or writes to a memory location outside the buffer's intended boundary. This may result in read or write operations on unexpected memory locations that could be linked to other variables, data structures, or internal program data.