This actually also has to do with cross protocol attacks. http://i8jesus.com/?p=75
Re:65k Open TCP Ports
by maximusprime on Thursday October 20, 2011 @03:57AM
(#3133920)
There was an attack last year on freenode which worked like this... javascript did an automatic POST to irc.freenode.net:6667 with form data that included IRC commands to spam channels etc.
Unfortunately at the time their ircd didn't care about the 'POST / HTTP headers', and lovingly accepted the spam.
(PS: HN shows extra characters than what I typed in that HTML. Might be an XSS vulnerability in there.)