Re: [TLS] RFC-4366-bis and the unrecognized_name(112) alert

Michael D'Errico <mike-list@pobox.com> Tue, 25 May 2010 17:58 UTC

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Date: Tue, 25 May 2010 10:58:17 -0700
From: Michael D'Errico <mike-list@pobox.com>
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Subject: Re: [TLS] RFC-4366-bis and the unrecognized_name(112) alert
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Martin Rex wrote:
> Michael D'Errico wrote:
>> In my server code, the SNI is checked to see if there is a matching
>> virtual host with that domain name.  If there is, then no alert is
>> sent.  If there is no matching virtual host, then it checks whether
>> there is a default virtual host set up.  If there is a default, then
>> an unrecognized_name alert is sent with the warning level.  When no
>> default is configured, the alert sent is fatal since the handshake
>> can not continue.
>>
>> The warning lets the client know that there was not a match, but that
>> the server can still continue using its default.
> 
> 
> While this behaviour appears quite sensible/plausible, it will lead
> to the behaviour in the wild that Yngve is reporting.
> 
> An application which
> does not configure any SNI characteristics, is not using SNI, and
> for these, the server TLS implementation should _NOT_ be sending
> SNI mismatch TLS alerts unless the application explicitly requests so.

My server code will not send an alert unless the client (a) sent an
SNI and (b) that SNI did not map to a virtual host.

So that should not cause a problem.

It might be a good idea to clarify when sending an unrecognized_name
alert would be appropriate and clarify that it can be just a warning
and what that means.

Mike