Problem with mysql backend and SSL ciphers

[Aki Tuomi]

On 17.4.2019 23.00, Kostya Vasilyev via dovecot wrote:
> I'm not Aki but hope you don't mind...
>
> On Wed, Apr 17, 2019, at 10:42 PM, TG Servers via dovecot wrote:
>> Hi,
>>
>> MariaDB documentation says it accepts OpenSSL cipher strings in its
>> ssl_cipher parameters like ssl_cipher="TLSv1.2".
>> This is also mentioned when creating or changing users in terms of
>> setting this with the REQUIRE CIPHER parameter like CREATE USER ...
>> REQUIRE CIPHER 'TLSv1.2'...
>> So this is all very nice and also working but sadly whith a
>> connection string from dovecot it is not working anymore.
>> If you set the user only on REQUIRE SSL, the ssl connection and
>> everything is working fine between dovecot and mariaDB.
>> But when you set REQUIRE CIPHER 'TLSv1.2' in mariaDB and use
>> ssl_cipher=TLSv1.2 in the connection string from dovecot you get the
>> following errors, it does not account the various ciphers of TLSv1.2
>> but rather expects TLSv1.2 somehow.
>>
>> [Note] X509 ciphers mismatch: should be 'TLSv1.2' but is
>> 'DHE-RSA-AES256-GCM-SHA384'
>>
>> A good cipher is sent but the cipher cannot be TLSv1.2 of course :)
>> But no one will put in explicit ciphers there as this is dangerous in
>> my eyes, people forget updating... Also this is misbehaviour or
>> misdocumented.
>> The thing is now where to address this. Dovecot or MariaDB.
>> As dovecot seems to use a good cipher and MariaDB expects a TLSv1.2
>> string rather than a cipher out of TLSv1.2 I would say mariaDB but am
>> not sure.
>>
>> Maybe Aki could say something to it, would be great.
>>
>> Thanks!
>>
>> The docs from mariaDB to this are here :
>> https://mariadb.com/kb/en/library/create-user/
>> https://mariadb.com/kb/en/library/securing-connections-for-client-and-server/
>
> But but but...
>
> TLSv1.2 is not a cipher, it's a protocol.
>
> Maria DB docs say the settings excepts a list of ciphers or a protocol
> name:
>
> https://mariadb.com/kb/en/library/ssltls-system-variables/#ssl_cipher
>
> In in other software it's common to have two distinct settings, one
> for protocol and one a cipher "pattern".
>
> Maybe you could try something like this:
>
> kECDHE+CHACHA20:kECDHE+AESGCM
>
> ChaCha / Poly and AES GCM are TLS 1.2 + only ciphers.
>
> This will not include AES CBC which exist with variations in both 1.0
> to 1.2, but if you're security conscious, you probably don't want to
> use CBC anyway.
>
> Or you could match just 1.2 versions with - I think -
> AESCBC+SHA384:AESCBC+SHA256. This will leave out AES CBC SHA1 which
> are in 1.0 - 1.1.
>
> And now Aki can correct me :)
>
> -- K
>

All I'm going to say is that this is 100% mysql/mariadb issue.

Aki

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