FFmpeg Heap Buffer Overflow in VC-2/Dirac RTP Packetizer

FFmpeg before commit 1cdeb3c contains a heap buffer overflow vulnerability in the VC-2/Dirac RTP packetizer (libavformat/rtpenc_vc2hq.c) that allows attackers to trigger memory corruption by supplying a crafted Dirac data unit. The packetizer copies an input-derived data unit or fragment size into a fixed-size buffer without an upper bound check, causing a heap buffer overflow when the crafted input is packetized for RTP output.