Prior to ffmpeg version 4.3, the tty demuxer did not have a 'read_probe' function assigned to it. By crafting a legitimate "ffconcat" file that references an image, followed by a file the triggers the tty demuxer, the contents of the second file will be copied into the output file verbatim (as long as the -vcodec copy option is passed to ffmpeg).
[
{
"digest": {
"threshold": 0.9,
"line_hashes": [
"87847563956555810086109357068916520368",
"179033659746351296284011130959867098470",
"29912285464798826292798173282494127710",
"149942135119221602751422759954712516314",
"122614738720108430322534464033586885784",
"264754942809671600674997705643627881480",
"46529893056919444838326796542476614873",
"232657199141909422124284627650612937300",
"176347224354873379396459371193661897034",
"324250718937501476783835246937268406065",
"230021871174800559649899559161600728586",
"71857368728975087535349751898191175066"
]
},
"signature_type": "Line",
"target": {
"file": "libavformat/tty.c"
},
"deprecated": false,
"source": "https://github.com/ffmpeg/ffmpeg/commit/3bce9e9b3ea35c54bacccc793d7da99ea5157532",
"signature_version": "v1",
"id": "CVE-2021-3566-b3a97196"
}
]