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Re: [TLS] cross-domain cache sharing and 0rtt

Ilari Liusvaara <ilariliusvaara@welho.com> Thu, 05 January 2017 08:05 UTC

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Date: Thu, 05 Jan 2017 10:05:18 +0200
From: Ilari Liusvaara <ilariliusvaara@welho.com>
To: Benjamin Kaduk <bkaduk@akamai.com>
Message-ID: <20170105080518.GA23934@LK-Perkele-V2.elisa-laajakaista.fi>
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Cc: Adam Langley <agl@imperialviolet.org>, "tls@ietf.org" <tls@ietf.org>
Subject: Re: [TLS] cross-domain cache sharing and 0rtt
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On Wed, Jan 04, 2017 at 03:48:25PM -0600, Benjamin Kaduk wrote:
> On 01/03/2017 10:38 PM, Martin Thomson wrote:
> 
> %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
> 
> When a server has valid credentials for multiple server names, and at
> least one of those names could also be served by valid credentials on a
> different server, it may be possible for an attacker
> to replay traffic from a client intended for the second server against
> the first server, including 0-RTT data.  This behavior can be avoided if
> the server knows what server name is expected for a given request (e.g.,
> via an HTTP Host header) and verifies that the supplied SNI extension
> matches the expected server name, though in some cases the mismatch is
> harmless.
> 
> %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

Checking that Host/:authority and SNI match does not work properly for
HTTP/2.

There, if you want to avoid default-vhost attacks, you have to check
:authority (Host) without reference to SNI.



-Ilari

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