Re: [TLS] SSL Renegotiation DOS

Joe Orton <> Tue, 15 March 2011 15:38 UTC

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Date: Tue, 15 Mar 2011 15:39:43 +0000
From: Joe Orton <>
To: Steve Dispensa <>
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Subject: Re: [TLS] SSL Renegotiation DOS
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On Tue, Mar 15, 2011 at 08:23:44AM -0500, Steve Dispensa wrote:
> >  I'm curious, what is the effect of that in typical HTTPS servers? 
> > Do servers allow for renegotiation initiated by the client? (apache 
> > with mod_gnutls doesn't)
> When we looked at implementations last year, we found that IIS was 
> definitely not willing to do client-initiated renegotiation, but at 
> the time there were a few that would. I'm sure a lot has changed since 
> I last looked at it.

As part of the workaround for CVE-2009-3555 added in the 2.2.15 release 
of Apache httpd, mod_ssl will (or should!) reject any renegotiation 
initiated by the client.  The code still behaves this way, for both 
clients which support RFC 5746 and those which do not.

Older versions of Apache httpd/mod_ssl will allow a client-initiated 
reneg at any time, as is the default behaviour with OpenSSL-based 

I recall a complaint that some mobile browser was known to initiate 
renegs, but I can't find a reference for that; it might have been 
off-line discussion.  I'd be interested to hear any further data on 

Regards, Joe