tls_high_cipherlist with !SEED is ignored

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tls_high_cipherlist with !SEED is ignored

Stefan Bauer-2
Nessus reports for example TLS_RSA_WITH_SEED_CBC_SHA as weak on our submission port. So i was using the following to disable all SEED ciphers on submission port but it has no effect:

 -o smtpd_tls_mandatory_ciphers=high
 -o tls_preempt_cipherlist=yes
 -o tls_high_cipherlist=EDH+CAMELLIA:EDH+aRSA:EECDH+aRSA+AESGCM:EECDH+aRSA+SHA384:EECDH+aRSA+SHA256:EECDH:+CAMELLIA256:+AES256:+CAMELLIA128:+AES128:+SSLv3:!aNULL:!eNULL:!LOW:!3DES:!MD5:!EXP:!PSK:!DSS:!RC4:!SEED:!ECDSA:CAMELLIA256-S
HA:AES256-SHA:CAMELLIA128-SHA:AES128-SHA

after postfix restart,

nmap --script ssl-enum-ciphers -p 587 mailserver

still reports SEED ciphers:

$ nmap --script ssl-enum-ciphers -p 587 mailserver | grep SEED
|       TLS_DH_anon_WITH_SEED_CBC_SHA - F
|       TLS_DHE_RSA_WITH_SEED_CBC_SHA (dh 2048) - A
|       TLS_RSA_WITH_SEED_CBC_SHA (rsa 2048) - A
|       TLS_DH_anon_WITH_SEED_CBC_SHA - F
|       TLS_DHE_RSA_WITH_SEED_CBC_SHA (dh 2048) - A
|       TLS_RSA_WITH_SEED_CBC_SHA (rsa 2048) - A
|       TLS_DH_anon_WITH_SEED_CBC_SHA - F
|       TLS_DHE_RSA_WITH_SEED_CBC_SHA (dh 2048) - A
|       TLS_RSA_WITH_SEED_CBC_SHA (rsa 2048) - A


What am i missing?
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Re: tls_high_cipherlist with !SEED is ignored

Wietse Venema
stefan Bauer:
> Nessus reports for example TLS_RSA_WITH_SEED_CBC_SHA as weak on our
> submission port. So i was using the following to disable all SEED ciphers
> on submission port but it has no effect:
>
>  -o smtpd_tls_mandatory_ciphers=high
>  -o tls_preempt_cipherlist=yes
>  -o
> tls_high_cipherlist=EDH+CAMELLIA:EDH+aRSA:EECDH+aRSA+AESGCM:EECDH+aRSA+SHA384:EECDH+aRSA+SHA256:EECDH:+CAMELLIA256:+AES256:+CAMELLIA128:+AES128:+SSLv3:!aNULL:!eNULL:!LOW:!3DES:!MD5:!EXP:!PSK:!DSS:!RC4:!SEED:!ECDSA:CAMELLIA256-S
> HA:AES256-SHA:CAMELLIA128-SHA:AES128-SHA

I see no evidence that smtpd is using mandatory TLS, which I think
is a prerequisite for the above settings to have an observable effect.

        Wietse
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Re: tls_high_cipherlist with !SEED is ignored

Viktor Dukhovni
In reply to this post by Stefan Bauer-2
> On Jan 15, 2019, at 8:39 AM, Stefan Bauer <[hidden email]> wrote:
>
>  -o smtpd_tls_mandatory_ciphers=high
>  -o tls_preempt_cipherlist=yes
>  -o tls_high_cipherlist=EDH+CAMELLIA:EDH+aRSA:EECDH+aRSA+AESGCM:EECDH+aRSA+SHA384:EECDH+aRSA+SHA256:EECDH:+CAMELLIA256:+AES256:+CAMELLIA128:+AES128:+SSLv3:!aNULL:!eNULL:!LOW:!3DES:!MD5:!EXP:!PSK:!DSS:!RC4:!SEED:!ECDSA:CAMELLIA256-S
> HA:AES256-SHA:CAMELLIA128-SHA:AES128-SHA

Instead, try:

  master.cf:
        submission inet ... smtpd
          ...
          -o smtpd_tls_security_level=encrypt
          -o smtpd_tls_mandatory_ciphers=high
          -o smtpd_tls_exclude_ciphers=$msa_exclude_ciphers

  main.cf:
        msa_exclude_ciphers = SEED

See: http://www.postfix.org/postconf.5.html#smtpd_tls_exclude_ciphers

--
        Viktor.

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Re: tls_high_cipherlist with !SEED is ignored

Stefan Bauer-2
I just want to set allowed ciphers but can not enforce encryption generally. this seems to be a limitation and not possible right?

Am Dienstag, 15. Januar 2019 schrieb Viktor Dukhovni <[hidden email]>:

>> On Jan 15, 2019, at 8:39 AM, Stefan Bauer <[hidden email]> wrote:
>>
>>  -o smtpd_tls_mandatory_ciphers=high
>>  -o tls_preempt_cipherlist=yes
>>  -o tls_high_cipherlist=EDH+CAMELLIA:EDH+aRSA:EECDH+aRSA+AESGCM:EECDH+aRSA+SHA384:EECDH+aRSA+SHA256:EECDH:+CAMELLIA256:+AES256:+CAMELLIA128:+AES128:+SSLv3:!aNULL:!eNULL:!LOW:!3DES:!MD5:!EXP:!PSK:!DSS:!RC4:!SEED:!ECDSA:CAMELLIA256-S
>> HA:AES256-SHA:CAMELLIA128-SHA:AES128-SHA
>
> Instead, try:
>
>   master.cf:
>         submission inet ... smtpd
>           ...
>           -o smtpd_tls_security_level=encrypt
>           -o smtpd_tls_mandatory_ciphers=high
>           -o smtpd_tls_exclude_ciphers=$msa_exclude_ciphers
>
>   main.cf:
>         msa_exclude_ciphers = SEED
>
> See: http://www.postfix.org/postconf.5.html#smtpd_tls_exclude_ciphers
>
> --
>         Viktor.
>
>
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Re: tls_high_cipherlist with !SEED is ignored

Stefan Bauer-2
In reply to this post by Viktor Dukhovni
now i got it. sorry and thank you for your help.

Am Dienstag, 15. Januar 2019 schrieb Viktor Dukhovni <[hidden email]>:

>> On Jan 15, 2019, at 8:39 AM, Stefan Bauer <[hidden email]> wrote:
>>
>>  -o smtpd_tls_mandatory_ciphers=high
>>  -o tls_preempt_cipherlist=yes
>>  -o tls_high_cipherlist=EDH+CAMELLIA:EDH+aRSA:EECDH+aRSA+AESGCM:EECDH+aRSA+SHA384:EECDH+aRSA+SHA256:EECDH:+CAMELLIA256:+AES256:+CAMELLIA128:+AES128:+SSLv3:!aNULL:!eNULL:!LOW:!3DES:!MD5:!EXP:!PSK:!DSS:!RC4:!SEED:!ECDSA:CAMELLIA256-S
>> HA:AES256-SHA:CAMELLIA128-SHA:AES128-SHA
>
> Instead, try:
>
>   master.cf:
>         submission inet ... smtpd
>           ...
>           -o smtpd_tls_security_level=encrypt
>           -o smtpd_tls_mandatory_ciphers=high
>           -o smtpd_tls_exclude_ciphers=$msa_exclude_ciphers
>
>   main.cf:
>         msa_exclude_ciphers = SEED
>
> See: http://www.postfix.org/postconf.5.html#smtpd_tls_exclude_ciphers
>
> --
>         Viktor.
>
>
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Re: tls_high_cipherlist with !SEED is ignored

Viktor Dukhovni
In reply to this post by Stefan Bauer-2
> On Jan 15, 2019, at 3:39 PM, Stefan Bauer <[hidden email]> wrote:
>
> I just want to set allowed ciphers but can not enforce encryption generally.

You cannot enforce encryption on the submission port?  Why not?

> this seems to be a limitation and not possible right?

The ciphers are configurable, but the recommended interface for most users
is to specify exclusions from the low level cipherlists, rather than deal
with their non-trivial syntax.

--
        Viktor.