Just because it’s not public facing doesn’t mean that it’s not an issue. It might be less of an issue, but it is still a massive vulnerability.
All it takes is one misconfiguration or other vulnerable system to use this as a jumping off point to burrow into other systems. Especially if this system has elevated access to sensitive locations within your network.
Desktop: Windows XP
Linux: Probably Raspbian on a Pi 2 b
Tech has come a long way since then lol