confused with ssl settings and some error - need help

Thu Apr 27 11:34:30 EEST 2017

Cipher list which You post provide better compatibility or security than
those which I currently have?
On older software version these cipher list works well and not generate any
errors when I run Internal PCI scan test from https://cloud.tenable.com for
another server. But for new server with newer software during test I got
errors in mail.err.

2017-04-27 10:00 GMT+02:00 Aki Tuomi <aki.tuomi at dovecot.fi>:

>
> > On April 27, 2017 at 10:55 AM Poliman - Serwis <serwis at poliman.pl>
> wrote:
> >
> >
> > Thank You for answers. But:
> > 1. How should be properly configured ssl_cipher_list?
>
> ssl_cipher_list = ALL:!kRSA:!SRP:!kDHd:!DSS:!aNULL:!eNULL:!EXPORT:!DES:!
> 3DES:!MD5:!PSK:!RC4:!ADH:!LOW at STRENGTH
>
> To disable non-EC DH, use:
>
> ssl_cipher_list = ALL:!DH:!kRSA:!SRP:!kDHd:!DSS:
> !aNULL:!eNULL:!EXPORT:!DES:!3DES:!MD5:!PSK:!RC4:!ADH:!LOW at STRENGTH
>
> > 2. Ok, removed !TLSv1 !TLSv1.1.
> > 3. Strange thing with ssl_protocols and ssl_cipher_list, because on older
> > server on Ubuntu 14.04 LTS, dovecot 2.2.9 and postfix 2.11.0 these two
> > lines looks exactly this same and no errors in mail.err file and mailes
> > works without any problem.
> > 4. No, currently I don't use LMTP.
>
> it is possible that postfix is not causing this error.
>
> >
> > 2017-04-27 8:25 GMT+02:00 Aki Tuomi <aki.tuomi at dovecot.fi>:
> >
> > >
> > > > On April 27, 2017 at 8:12 AM Poliman - Serwis <serwis at poliman.pl>
> wrote:
> > > >
> > > >
> > > > Hi,
> > > > To default dovecot.conf file I added (based on found documentation):
> > > > ssl = required
> > > > disable_plaintext_auth = yes     #change default 'no' to 'yes'
> > > > ssl_prefer_server_ciphers = yes
> > > > ssl_options = no_compression
> > > > ssl_dh_parameters_length = 2048
> > > > ssl_cipher_list =
> > > > ECDHE-RSA-AES128-GCM-SHA256:ECDHE-ECDSA-AES128-GCM-SHA256:
> > > ECDHE-RSA-AES256-GCM-SHA384:ECDHE-ECDSA-AES256-GCM-SHA384:
> > > DHE-RSA-AES128-GCM-SHA256:DHE-DSS-AES128-GCM-SHA256:kEDH+
> > > AESGCM:ECDHE-RSA-AES128-SHA256:ECDHE-ECDSA-AES128-
> > > SHA256:ECDHE-RSA-AES128-SHA:ECDHE-ECDSA-AES128-SHA:ECDHE-
> > > RSA-AES256-SHA384:ECDHE-ECDSA-AES256-SHA384:ECDHE-RSA-
> > > AES256-SHA:ECDHE-ECDSA-AES256-SHA:DHE-RSA-AES128-SHA256:DHE-
> > > RSA-AES128-SHA:DHE-DSS-AES128-SHA256:DHE-RSA-AES256-SHA256:
> > > DHE-DSS-AES256-SHA:DHE-RSA-AES256-SHA:AES128-GCM-SHA256:
> > > AES256-GCM-SHA384:AES128-SHA256:AES256-SHA256:AES128-
> > > SHA:AES256-SHA:AES:CAMELLIA:!aNULL:!eNULL:!EXPORT:!DES:!
> > > RC4:!MD5:!PSK:!aECDH:!EDH-DSS-DES-CBC3-SHA:!EDH-RSA-DES-
> > > CBC3-SHA:!KRB5-DES-CBC3-SHA
> > > >
> > >
> > > This looks rather cumbersome way to define ciphers.
> > >
> > > > 1. Are these settings good or can be improved?
> > > > 2. Is this line proper:
> > > > ssl_protocols = !SSLv2 !SSLv3 !TLSv1 !TLSv1.1
> > >
> > > Well if you only want to support TLSv1.2, which might lead into
> trouble.
> > >
> > > > or maybe should be:
> > > > ssl_protocols = !SSLv2 !SSLv3
> > > > 3. Last thing. I have below errors (they appear in loop in mail.err
> log
> > > > file):
> > > > #Apr 25 14:08:09 serwer-1 dovecot: imap-login: Error: SSL: Stacked
> error:
> > > > error:140760FC:SSL routines:SSL23_GET_CLIENT_HELLO:unknown protocol
> > > > #Apr 25 14:08:09 serwer-1 dovecot: imap-login: Error: SSL: Stacked
> error:
> > > > error:1408A10B:SSL routines:ssl3_get_client_hello:wrong version
> number
> > > > #Apr 25 14:08:51 serwer-1 dovecot: imap-login: Error: SSL: Stacked
> error:
> > > > error:1408F119:SSL routines:SSL3_GET_RECORD:decryption failed or bad
> > > record
> > > > mac
> > > > #Apr 25 14:08:51 serwer-1 dovecot: imap-login: Error: SSL: Stacked
> error:
> > > > error:1408A0C1:SSL routines:ssl3_get_client_hello:no shared cipher
> > >
> > > This means your client did not support your enabled ciphers.
> > >
> > > >
> > > > When I setup in postfix main.cf file (other lines default):
> > > > tls_ssl_options = no_ticket, no_compression
> > > > tls_preempt_cipherlist = yes
> > > > smtpd_sasl_security_options=noanonymous,noplaintext
> > > > smtpd_sasl_tls_security_options=noanonymous,noplaintext
> > > > smtpd_tls_mandatory_ciphers = high
> > > > smtpd_tls_dh1024_param_file = /etc/postfix/dh2048.pem
> > > > #instead of below I tried smtpd_tls_mandatory_exclude_ciphers but I
> > > don't
> > > > know what should be setup
> > > > smtpd_tls_exclude_ciphers = aNULL, eNULL, EXPORT, DES, RC4, MD5, PSK,
> > > > aECDH, EDH-DSS-DES-CBC3-SHA, EDH-RSA-DES-CBC3-SHA,
> > > ECDHE-RSA-DES-CBC3-SHA,
> > > > DES-CBC3-SHA, RC4-MD5, RC4-SHA, ECDHE-RSA-RC4-SHA
> > > > smtp_tls_exclude_ciphers = aNULL, eNULL, EXPORT, DES, RC4, MD5, PSK,
> > > aECDH,
> > > > EDH-DSS-DES-CBC3-SHA, EDH-RSA-DES-CBC3-SHA, ECDHE-RSA-DES-CBC3-SHA,
> > > > DES-CBC3-SHA, RC4-MD5, RC4-SHA, ECDHE-RSA-RC4-SHA
> > > >
> > > > Is between dovecot and postfix some communication using above
> ciphers or
> > > > something that generate that errors in log or maybe some public
> client
> > > try
> > > > connect and can't establish connection?
> > > >
> > >
> > > If you are using LMTP, then some of those settings will cause changes
> in
> > > how LMTP works as well.
> > >
> > >
> > > > Server with Ubuntu 16.04 LTS, postfix 3.1 and dovecot 2.2.22 and
> openssl
> > > > 1.0.2k.
> > > > --
> > > >
> > > > *Pozdrawiam / Best Regards*
> > > > *Piotr Bracha*
> > > >
> > > >
> > > >
> > > >
> > > > *tel. 534 555 877*
> > > >
> > > > *serwis at poliman.pl <serwis at poliman.pl>*
> > >
> > > Aki
> > >
> >
> >
> >
> > --
> >
> > *Pozdrawiam / Best Regards*
> > *Piotr Bracha*
> >
> >
> >
> >
> > *tel. 534 555 877*
> >
> > *serwis at poliman.pl <serwis at poliman.pl>*
>

-- 

*Pozdrawiam / Best Regards*
*Piotr Bracha*

*tel. 534 555 877*

*serwis at poliman.pl <serwis at poliman.pl>*