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A repost from r/linuxmemes - Because I saw the original comic
(thelemmy.club)
Luigi (with Linux Mint logo) and Mario (Ubuntu logo) come in
Mother: It's-a the Ubuntu Bros!
Linux Mint (Luigi): Mama why-a you never remember my name?
Mother: I'm-a sorry Green Ubuntu
Yup, and if some bad software wants to create malicious webserver they can not do it as all the ports that are open are used in a legit way. And thus can not really communicate either one or the other way.
A webserver listens on port 80 or 443. Neither port can be claimed by a normal user (no port below 1024 can). But yes if you manage more than your own user on a desktop AND these other users are not allowed to start programs on their own THEN a firewall can be helpful; but this is not a normal situation for a desktop-client, isn’t it?