I knew that localhost could be accessed, but the fact that local IP addresses on the LAN can be accessed is actually quite surprising to me. I suppose it makes sense, but it definitely makes me much more concerned with the security of local devices on my home and office networks now.

Are there any best-practices for keeping things locally safe (i.e. LAN devices like printers, testing boxes, tvs etc.) , beyond just treating them the same way you would an external facing machine?