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.
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