I use my ISP (Virgin in the UK) router which I, perhaps naively, assume is kept up to date with security patches. I don't use the wifi embedded in the router.
Hanging off the router I have a wifi access point running the latest available firmware which is roughly five years old (that is, the date on the firmware is about five years ago). Also I have some powerline adapters hanging off it which are quite old as well. Am I taking a big risk here, or is the fact that my elderly equipment is behind the NAT firewall in the router keeping me safe?
Moved to home networking, per OP request. :D
Now the response... you're as safe as anyone else with end-of-life consumer gear. :smug:
Put another way, is the vendor still maintaining and updating that wifi access point? If not, then as vulnerabilities are discovered, it will NOT be patched. And I don't necessarily trust the ISP 100% to be on top of proper updates for all of *their* gear, either. So, your main defense is that wifi access point, and it may be due for an upgrade, for security's sake.
The sad thing is, even with new equipment - if it's not being actively maintained with updates then it's as good as old equipment.
This is why I dont recommend cheap smartphones / tablets.
Though you can limit your attack surface by making the old equipment as dumb as possible for your needs (which is what I think you have done, by turning off the wifi). At that point I Think you're just using it as a layer 2 switch. Only IP accessible from inside your home network. Just make sure uPNP is turned off on the outside just in case.
yeah, my Netgear WIFI router sits behind my Cisco ASA 5525 firewall, it needs to be upgraded, but will require full reconfiguration after upgrade. that will cause a network outage. I probably should just buy a new one. and upgrade, then build a new WIFI network with new SSID. then migrate devices to new and decommission old