Many older all-in-one routers used to include Telnet access, and some gave the option of LAN only or LAN + WAN.
Most producers came to their senses long ago, but there may still be some configured that way and still in service.
I find this video and other articles I've found about the same problem to be sorely lacking and not understandable for anybody but those who know linux very well. I'm temped to say linux nerds only.
My main questions are (1) Does it apply to linux running on a PC?, and (2) Does it apply to cameras and/or NVRs? If anybody can address this, please do. Otherwise, I think it's useless information for almost everybody, because they don't understand if they're affected by it, much less how to fix it.
The best I can tell is it applies specifically to GNU InetUtils. I don't know if my linux systems and/or cameras have this even installed, and if so, if it's running.
The video above says there are over a billion devices running on linux. The warning in post #1 says 800,000 devices are exposed. That would mean that less than one out of 1,250 is exposed. Pretty low odds, and "exposed" doesn't mean compromised or hacked. But which 800,000 devices are in the one out of 1,250 group?