The custom get_buffer2 path is not something the attacker needs shell access to invoke. It is a normal public libavcodec API used by applications embedding FFmpeg. The attacker’s input is still just the crafted RASC/AVI media. The target application invokes FFmpeg/libavcodec during normal media processing. The PoC uses a custom buffer provider to make the heap layout deterministic and to place a demonstrable callback pointer next to the decoded PAL8 plane. That proves the bug can redirect control flow in a valid libavcodec decode flow. It does not mean the exact same file will pop calc under stock ffmpeg -i everywhere, but definitely not impossible. I popped a few shells today with it on a few websites for testing purposes. Reported it to them all, of course.