In the same style, I loved watching this finding walkthrough: https://www.youtube.com/watch?v=zjafMP7EgEA
It’s not too dense and gives a very good sense of the process of finding such exploits.
Almost every single router on the market has something like this. Interactive web interfaces are just massive security holes. If you let someone access it (e.g. if they can plug into your ethernet or use your wifi) you have effectively given them control over your whole network.
That was a really good crack. Nice work!