Heap-buffer-overflow write in FFmpeg SANM process_ftch
It is possible to cause an use-after-free write in SANM decoding with a carefully crafted animation using subversion <2.
When a STOR chunk is present, a subsequent FOBJ chunk will be saved in ctx->stored_frame. Stored frames can later be referenced by FTCH chunks. For files using subversion < 2, the undecoded frame is stored, and decoded again when the FTCH chunks are parsed. However, in process_frame_obj if the frame has an invalid size, there’s an early return, with a value of 0.
This causes the code in decode_frame to still store the raw frame buffer into ctx->stored_frame. Leaving ctx->has_dimensions set to false.
A subsequent chunk w