Re: [TLS] ALPN concerns

Yoav Nir <ynir@checkpoint.com> Wed, 06 November 2013 16:11 UTC

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From: Yoav Nir <ynir@checkpoint.com>
To: Peter Gutmann <p.gutmann@auckland.ac.nz>
Thread-Topic: [TLS] ALPN concerns
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Date: Wed, 6 Nov 2013 16:10:00 +0000
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Subject: Re: [TLS] ALPN concerns
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On Nov 5, 2013, at 10:52 PM, Peter Gutmann <p.gutmann@auckland.ac.nz>
 wrote:

> Brian Smith <brian@briansmith.org> writes:
> 
>> I am very concerned about the issues that they've run into where many web
>> servers are failing to handshake when the ClientHello message is larger than
>> 255 bytes.
> 
> I'm curious as to how something like this could come about, is anyone familiar
> with the code base for something that does this?  Is there actually code out
> there that explicitly checks:
> 
>  if( sizeof( client_handshake ) > 255 )
>    return( -1 );
> 
> and if so, why?

Based on no actual knowledge, maybe it's part of some anti-DoS scheme.

Big ClientHello --> Weird --> Attack