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Re: [TLS] Connection diversion to other subdomains

Florian Weimer <fweimer@bfk.de> Fri, 05 November 2010 16:14 UTC

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To: Marsh Ray <marsh@extendedsubset.com>
References: <4CC765D6.6020704@KingsMountain.com> <1288145780.6053.50.camel@mattlaptop2.local> <1288147744.6053.51.camel@mattlaptop2.local> <1288238488.2016.17.camel@mattlaptop2.local> <821v70m5i9.fsf@mid.bfk.de> <4CD42BAD.7080300@extendedsubset.com>
From: Florian Weimer <fweimer@bfk.de>
Date: Fri, 05 Nov 2010 16:14:48 +0000
In-Reply-To: <4CD42BAD.7080300@extendedsubset.com> (Marsh Ray's message of "Fri\, 05 Nov 2010 11\:07\:09 -0500")
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Cc: IETF TLS WG <tls@ietf.org>
Subject: Re: [TLS] Connection diversion to other subdomains
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* Marsh Ray:

> On 11/05/2010 05:25 AM, Florian Weimer wrote:
>> * Matt McCutchen:
>>
>>> I looked through my browser history for registered domains containing a
>>> TLS web server bearing a wildcard certificate and another subdomain on a
>>> different IP address.  In almost all cases, the server was willing to
>>> send me wrong content when I asked for the other subdomain via SNI and
>>> HTTP Host.  Strictly speaking, this is a vulnerability.  Usually the
>>> effect is just goofy, though on one major web site which I won't name,
>>> it led to XSS.
>>
>> How is this even possible given that browsers do not send such crafted
>> requests?
>
> DNS poisoning or any other means of TCP redirection.

Ah, I misread Matt's comment, I thought he was referring to Host (SNI)
/= Host (HTTP header).

Yes, obviously, your wildcard certificate is more trusted than your
host-specific certificate, and this has to be reflected in the server
setup etc.  I can see that reality is quite different from that.  (The
problem that your ad servers are the most trusted node on your network
is a similar phenomenon.)

-- 
Florian Weimer                <fweimer@bfk.de>
BFK edv-consulting GmbH       http://www.bfk.de/
Kriegsstraße 100              tel: +49-721-96201-1
D-76133 Karlsruhe             fax: +49-721-96201-99

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