On Thu, Mar 10, 2016 at 12:30 PM, Osiris <dovecot@flut.demon.nl> wrote:

On 09-03-16 13:14, djk wrote:

...

On 09/03/16 10:44, Florent B wrote:

...

Hi,

I don't see any SSL configuration option in Dovecot to disable "Client-initiated secure renegotiation".

It is advised to disable it as it can cause DDoS (CVE-2011-1473).

Is it possible to have this possibility through an SSL option or other ?

Thank you.

Florent ssl_protocols = !SSLv3 !SSLv2

Is that enough?

I'm afraid not. I've got SSLv2 and SSLv3 disabled and with openssl s_client -connect $host:993 I still can successfully renegotiate by passing a single 'R'.

Are you use good ssl_cipher_list (https://wiki.mozilla.org/Security/Server_Side_TLS)?

My config

Service options

10-ssl

ssl = yes ssl_cert = </etc/pki/tls/certs/.crt ssl_key = </etc/pki/tls/private/.key ssl_require_crl = no ssl_ca = </etc/pki/tls/cert.pem 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:ECDHE-RSA-DES-CBC3-SHA:ECDHE-ECDSA-DES-CBC3-SHA:AES128-GCM-SHA256:AES256-GCM-SHA384:AES128-SHA256:AES256-SHA256:AES128-SHA:AES256-SHA:AES:CAMELLIA:DES-CBC3-SHA:!aNULL:!eNULL:!EXPORT:!DES:!RC4:!MD5:!PSK:!aECDH:!EDH-DSS-DES-CBC3-SHA:!EDH-RSA-DES-CBC3-SHA:!KRB5-DES-CBC3-SHA ssl_parameters_regenerate = 72h

The !TLSv1 are OK, without TLS not work imtest (cyrus test suit)

ssl_protocols = !SSLv2 !SSLv3

Prefer the server's order of ciphers over client's

Only available on dovecot 2.2.6 and later::

ssl_prefer_server_ciphers = yes

Only available on dovecot 2.2.7 and later::

ssl_dh_parameters_length = 2048

Work fine, but only testssl.sh scanner generate small warning "Secure Client-Initiated Renegotiation VULNERABLE (NOT ok), DoS threat"

openssl s_client -connect $host:993 -ssl2(3) and openssl s_client -connect $host:143 -starttls imap -showcerts -state -crlf -ssl2(3) break connection

On 10.03.2016 12:40, Osiris wrote:

<snip/>

That's just the question of Florent: how to disable Secure Client-Initiated Renegotiation.

Hi!

There is no way to disable this in OpenSSL, and the CVE you refer to has been disputed. Please see http://cve.mitre.org/cgi-bin/cvename.cgi?name=cve-2011-1473 and https://www.openssl.org/docs/manmaster/ssl/SSL_CTX_set_options.html.

Without altering OpenSSL sources, secure renegotiations will take place.

Aki Tuomi Dovecot Oy