> replacing BANG with the title of _a_ video on this channel.

The agent has knowledge of private videos, so the proof of concept causes it to construct a URL that sends one video identity to the attacker which may be a private video. The attack could be improved to say "a recent private video", or to construct a long url param list of the most 10 most recent videos, etc. Sending any agent knowledge to an attacker is a vector to sending any agent knowledge to an attacker.