[tenacious_tuna]

This is a common function of uPnP, which I've seen as features in router config pages since the mid 2000s.

https://en.wikipedia.org/wiki/Universal_Plug_and_Play#NAT_tr...

[ectospheno]

Running a firewall with upnp enabled has always amused me. Might as well just turn the firewall off if you let any machine shoot any hole it wants in it.