After seeing this question I am wondering what could actually happen if a Windows XP machine was connected to a local network via WIFI. Imagine the machine will be used to browse the internet, read and write documents, so think of the usual basic tasks. I know WinXP is not supported anymore, and if I'm not mistaken I think some software (like Chrome) can't even be updated on such OS because the latest versions are not supported, so I know the threat comes from outdated software, but what I don't know is how exactly this threat can harm the local network.
I suppose it could be considered to be the same as having an attacker inside the local network, so the WinXP machine if infected could intercept, read, or modify all the traffic on the network (if not encrypted with TLS). Then portscanning, trying to find vulnerabilities in other machines connected to the same network. Am I right? Anything else?
I also wonder if this threat can be mitigated, or if the only way to deal with this is really to make sure that such an outdated machine is never connected to the network.