Simon Willison’s Weblog

MDN: Subdomain takeovers (via) MDN have a page about subdomain takeover attacks that focuses more on CNAME records: if you have a CNAME pointing to a common delegated hosting provider but haven’t yet provisioned your virtual host there, someone else might beat you to it and use it for an XSS attack.

“Preventing subdomain takeovers is a matter of order of operations in lifecycle management for virtual hosts and DNS.”

I now understand why Google Cloud make your “prove” your ownership of a domain before they’ll let you configure it to host e.g. a Cloud Run instance.