Your software doesn't get security patches, hackers find a way to abuse security holes to cause you harm.
Maybe they make your node stop working, maybe they find a way to break into your home network, maybe they do something else.
Discussion
Ok thanks, as for ddos I've never dealt with it but I know others have, but an attacker gaining access to a network via running bitcoin core I mean is this really a thing or just a what if
basically a "what-if" but if you stay tuned to the community, serious issues will come up as they are discovered. you can also just run your node when you need to transact or verify something.