It's not really jstrieb.github.io that's serving it, because since the content is in the url fragment, it is never sent to or from the server, it's handled entirely clientside.

>a very effective XSS host.

It can only do XSS against jstrieb.github.io which has nothing valuable. So it's not useful for anything. It can't be used in a <script> tag to obfuscate XSS attacks against other websites either, because the response isn't formatted as javascript. I guess it could be used in <iframes> on other websites in order to add obfuscation, but I think the use to attackers would be quite low.

You still need something to serve you the initial document.write js, unless you are going to convince people to open your links with locally saved "index.html". I called it "XSS" because you can execute arbitrary javascript, and I was trying to avoid bluntly calling it "malware".

Though I probably should have. Here is an example of a HackerNews login page served with jstrieb.github.com https://tinyurl.com/yypvh3by, you can login to news.ycombinator.com with it, but it easily could have been a phishing site.

My point is, this is a very good idea for offensive operations.

But someone could register the github account newsycombinator and then serve an identical phishing page at newsycombinator.github.io .

I guess you're right that it's useful for takedown resistance in phishing attacks. It's useless for small, sophisticated, targeted phishing attacks, but for large blunt untargeted phishing attacks it could be useful to have a site that would be difficult to take down and censor.

But I do consider phishing different than XSS.