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This DoS risk is documented in section 14.5 of the HSTS standard.

https://tools.ietf.org/html/rfc6797#section-14.5

It's true that HSTS could be a way for someone who can set up a seemingly valid but nonetheless fake HTTPS listener on a domain to prevent people from later communicating with a genuine HTTP service on that domain.

Three remedies for this, with different degrees of applicability to different sites:

* Put a CAA record for your domain into your DNS (see https://tools.ietf.org/html/rfc6844) to prevent legitimate certificate authorities from issuing the cert to the impostor. (This only provides protection if the attacker doesn't control your DNS zone.)

* Actually switch to HTTPS!

* If this attack happens to you and you don't want to switch to HTTPS, run a legitimate HTTPS listener on your domain that clears the HSTS status and then redirects users back to HTTP.



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