[TicklishTiger]

This is not called XSS.

This is just user generated html on subdomains.

Github does the same on github.io. Everybody can make a theirname.github.io page and alert whatever they like too.

So does Gitlab on yourname.gitlab.io, Wordpress on yourname.wordpress.com etc. It is a common practice.

[y4mi]

Agreed.

That's only an issue if this is possible for comments. The current behavior is working as intended I'd say.