Restricting SSL/TLS protocol versions on Dovecot 2.2.22

[Reio Remma]

On 30.07.2018 22:29, Aki Tuomi wrote:
>> On 30 July 2018 at 21:42 J Doe <general at nativemethods.com> wrote:
>>
>>
>>
>>> On Jul 29, 2018, at 6:02 PM, Alexander Dalloz <ad+lists at uni-x.org> wrote:
>>>
>>> Am 29.07.2018 um 21:02 schrieb J Doe:
>>>> Hello,
>>>> I have a question regarding SSL/TLS settings for Dovecot version 2.2.22.
>>>> In: 10-ssl.conf there are two parameters:
>>>>      ssl_protocols
>>>>      ssl_cipher_list
>>>> ssl_protocols is commented with “SSL protocol to use” and ssl_cipher_list is commented with “SSL ciphers to use”.
>>>> If I want to disable SSLv3, for example, do I need to use both parameters or will disabling SSLv3 ciphers in
>>>> ssl_cipher_list do the same thing ?
>>>> So is:
>>>>      ssl_cipher_list = !SSLv3
>>>> …equivalent to:
>>>>      ssl_protocols = !SSLv3
>>>>      ssl_cipher_list = !SSLv3
>>>
>>> No. SSLv3 is not a cipher but a protocol.
>>>
>>> "ssl_protocols = !SSLv2 !SSLv3" is what you want to specify.
>>>
>>> For ciphers you could define by ssl_cipher_list see "openssl ciphers -v”
>> Hi Alexander and list,
>>
>> I think there may be a discrepancy in the documentation.
>>
>> On the wiki on the “Dovecot SSL Configuration” page [1] under the section “SSL security settings” it says:
>>
>>      ssl_cipher_list = ALL:!LOW:!SSLv2:!EXP:!aNULL
>>
>> In the conf.d/10-ssl.conf it states:
>>
>>      # SSL protocols to use
>>      #ssl_protocols = !SSLv2
>>
>>      # SSL ciphers to use
>>      #ssl_cipher_list = ALL:!LOW:!SSLv2:!EXP:!aNULL
>>
>> My new question is:
>>
>>      1. Are the SSL/TLS protocols to use and/or exclude specified in “ssl_protocols”, “ssl_cipher_list” or both ?
>>
> You can use SSLv2 ciphers with TLSv1.2 protocol, if enabled. ssl protocol defines which protocol(s) to support. ssl_cipher_list defines which cipher(s) to support. They are not the same thing.
>
> Aki

I personally used https://www.ssllabs.com/ssltest/analyze.html when I 
set up my server to get green across the board for the web server and 
then used the same ciphers for Dovecot and confirmed the result with 
https://github.com/drwetter/testssl.sh

ssl_min_protocol = TLSv1 # New in Dovecot 2.3 iirc.
ssl_cipher_list = "EECDH+ECDSA+AESGCM EECDH+aRSA+AESGCM 
EECDH+ECDSA+SHA384 EECDH+ECDSA+SHA256 EECDH+aRSA+SHA384 
EECDH+aRSA+SHA256 EECDH+aRSA+RC4 EECDH EDH+aRSA RC4 !aNULL !eNULL !LOW 
!3DES !MD5 !EXP !PSK !SRP !DSS !RC4 !SEED"
ssl_prefer_server_ciphers = yes

Good luck,
Reio