I see you have got root on thenotebook and you said to DM you for a hint. I'm pretty sure I know what to do in that I can run docker exec as sudo and I need to use CVE-2019-5736 which overwrites runc. However I've tried several payloads on github:
Changing the code in both to send me a reverse shell but neither worked. What am I missing? Am I on the right lines?