There are certainly a lot of forms that this should not work on, I think it's a stretch to say that no forms on the internet should let this work. The login fo

There are certainly a lot of forms that this should not work on, I think it's a stretch to say that no forms on the internet should let this work. The login form on news.ycombinator.com even works: You could try: http://getposted.io/post?action=https://news.ycombinator.com/login&acct=nathancahill&pw=YourPassword http://getposted.io/post?action=https://news.ycombinator.com... But you shouldn't. That use case is specifically why I bring up the privacy issues surrounding using it.