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Re: [Acme] Alternative proposal for fixing TLS-SNI / revisiting HTTPS-01 authorization

Ilari Liusvaara <ilariliusvaara@welho.com> Fri, 12 January 2018 17:08 UTC

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Date: Fri, 12 Jan 2018 19:08:47 +0200
From: Ilari Liusvaara <ilariliusvaara@welho.com>
To: "Gerd v. Egidy" <gerd.von.egidy@intra2net.com>
Cc: acme@ietf.org
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Subject: Re: [Acme] Alternative proposal for fixing TLS-SNI / revisiting HTTPS-01 authorization
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On Fri, Jan 12, 2018 at 06:03:34PM +0100, Gerd v. Egidy wrote:
> > That is still vulernable to default-vhost issues if:
> > 
> > - The hoster does not explicitly reserve default vhost (I have seen that
> >   kind of behavior with http:// too).
> > - The hoster lets customers upload arbitrary certificates.
> 
> I think you also need:
> 
> - A user is able to trick the server into serving his document root as default 
> vhost
> 
> - The webserver serves the default tls vhost, even if the CA requested a 
> specific vhost via SNI

Well, I think both are impiled by default vhost.
 
> > (And there are countermeasures that can detect default vhosts).
> 
> Could you explain in more detail?
> 
> Will they still work in conjunction with TLS and SNI?

One trick: Use some wild host value, and see that either TLS handshake
fails with alert 112, or that returned certificate is different.


-Ilari

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