I have a router set up just for my wifi cameras. The router is not plugged into the internet, but it is directly connected to one of two Ethernet ports on my ×86 home assistant server. The other Ethernet port for Home Assistant is connected to the internet. Is there any chance a device connected that router could somehow access the internet from homeassistant?
Unless you actually make the homeassistant server into a bridge it wouldn’t on the network layer. Ideally you would prevent any inbound connections from the offline network (so it cant use any open ports there to try and pivot). But yeah really unlikely.