Extra intermediate certificate when using ssl_alt_cert

[Aki Tuomi]

> On 10 March 2018 at 16:05 Aki Tuomi <aki.tuomi at dovecot.fi> wrote:
> 
> 
> 
> > On 10 March 2018 at 15:20 John Fawcett <john at voipsupport.it> wrote:
> > 
> > 
> > On 10/03/18 14:06, Aki Tuomi wrote:
> > >
> > >> On 10 March 2018 at 14:49 John Fawcett < john at voipsupport.it
> > >> <mailto:john at voipsupport.it>> wrote:
> > >>
> > >>
> > >> On 08/03/18 18:43, Peter Linss wrote:
> > >>> I just added an ECDSA certificate to my mail server using
> > >>> ssl_alt_cert (the RSA certificate is specified by ssl_cert), both
> > >>> certificate files contain the certificate and a single intermediate
> > >>> (which currently happens to be the same intermediate from Let’s
> > >>> Encrypt).
> > >>> When connecting to the server using either RSA or ECDSA ciphers, the
> > >>> server sends the proper certificate, but also sends two
> > >>> intermediates. Apparently it’s reading the intermediate from both
> > >>> files and using both for all situations, rather than using only the
> > >>> intermediate in the RSA file for RSA certificates, and the
> > >>> intermediate in the ECDSA file for ECDSA certificates. I expect this
> > >>> will be a bigger problem when Let’s Encrypt starts using ECDSA
> > >>> intermediates.
> > >>> Removing the intermediate from the ssl_alt_cert file solves the
> > >>> problem (but then doesn’t allow an ECDSA intermediate to be specified).
> > >> I believe that supplying multiple unrelated intermediate certificates is
> > >> an incorrect behaviour, though I don't know if this is a problem that
> > >> can be solved in Dovecot or has to be addressed in openssl itself.
> > >>
> > >> Do you get any issue in certificate validation in the client?
> > >>
> > >> John
> > >
> > > You sure your cert file does not contain unrelated certificates?
> > > ---
> > > Aki Tuomi
> > 
> > Aki
> > 
> > I'll leave Peter to respond about his cert files, but in the test I did,
> > each the ssl_cert and ssl_alt_cert each contained the server cert and
> > the next cert in the chain. However, both intermediates were supplied
> > whether using RSA or ECDSA.
> > 
> > John
> >
> 
> I can confirm this behaviour. We'll look into it.
> 
> Aki

This appears to be slightly too difficult to fix for OpenSSL 1.0.0, but we can fix this for 1.0.2 and later on next release.

Aki