How to disable SSLv3

Revision as of 19:24, 15 October 2014 by Thom (talk | contribs) (8.0.x)

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This article applies to the following ZCS versions.

ZCS 8.0 Article ZCS 8.0 ZCS 8.5 Article ZCS 8.5

How to disable SSLv3

Due to the recent discovery of a new SSL vulnerability (CVE-2014-3566: Poodle SSLv3), this protocol has been considered unsafe. This is a protocol flaw and Zimbra might include patches or configuration changes in future releases. Please check existing Bug for more information.

As a workaround, this guide will help you on how to disable SSLv3 with Zimbra. This has been tested on both ZCS 8.0.8 and 8.5.0 releases.

Note: disabling SSLv3 might prevent older browsers to connect to Zimbra using SSL as they don't support TLS 1.0.

Postfix (MTA)


zmprov mcf zimbraMtaSmtpdTlsProtocols '!SSLv2,!SSLv3'


At the MTA server, run:

postconf -e smtpd_tls_protocols='!SSLv2,!SSLv3'

Run "zmmtactl stop ; zmmtactl start" to force the changes or wait for mailboxd to rewrite Postfix config from LDAP after 2 minutes.

Note that smtpd_tls_protocols will need to be set after every upgrade as there is no way to preserve them in ZCS 8.0 and previous.

Testing Postfix STARTTLS

Run openssl, forcing SSLv3:

openssl s_client -connect -ssl3 -starttls smtp

Confirm that connection is refused:

140701008086856:error:14094410:SSL routines:SSL3_READ_BYTES:sslv3 alert handshake failure:s3_pkt.c:1257:SSL alert number 40
140701008086856:error:1409E0E5:SSL routines:SSL3_WRITE_BYTES:ssl handshake failure:s3_pkt.c:596:
SSL handshake has read 220 bytes and written 0 bytes
New, (NONE), Cipher is (NONE)
Secure Renegotiation IS NOT supported
Compression: NONE
Expansion: NONE
   Protocol  : SSLv3
   Cipher    : 0000
   Key-Arg   : None
   Krb5 Principal: None
   PSK identity: None
   PSK identity hint: None
   Start Time: 1413400965
   Timeout   : 7200 (sec)
   Verify return code: 0 (ok)

Nginx (Proxy)


For https and Admin UI, please edit /opt/zimbra/conf/nginx/templates/nginx.conf.web.https.default.template and /opt/zimbra/conf/nginx/templates/nginx.conf.web.admin.default.template. Include the following line under the server { } configuration:

ssl_protocols TLSv1 TLSv1.1 TLSv1.2;


# HTTPS Proxy Default Configuration
    ssl_protocols TLSv1 TLSv1.1 TLSv1.2;
    ${core.ipboth.enabled}listen                  [::]:${web.https.port} default;


If you are using SSO with Client certificates, also edit /opt/zimbra/conf/nginx/templates/nginx.conf.web.sso.default.template.

For imaps and pop3s, please edit /opt/zimbra/conf/nginx/templates/nginx.conf.mail.pop3s.default.template and /conf/nginx/templates/nginx.conf.mail.imaps.default.template:


# POP3S proxy default configuration
    ssl_protocols TLSv1 TLSv1.1 TLSv1.2;


Restart the proxy servers with: "zmproxyctl stop ; zmproxyctl start"

Jetty (mailboxd)


How to verify if the changes have been done? We should run the following command (as zimbra) for every port using SSL:

openssl s_client -connect `zmhostname`:<port> -ssl3 |grep failure

Example, for port 443:

openssl s_client -connect `zmhostname`:443 -ssl3

If it shows a failure, it's good and we don't support SSLv3:

140532971947680:error:14094410:SSL routines:SSL3_READ_BYTES:sslv3 alert handshake failure:s3_pkt.c:1275:SSL alert number 40
140532971947680:error:1409E0E5:SSL routines:SSL3_WRITE_BYTES:ssl handshake failure:s3_pkt.c:598:

If you are seeing:

New, TLSv1/SSLv3, Cipher is ECDHE-RSA-AES128-SHA
Server public key is 2048 bit
Secure Renegotiation IS supported

SSLv3 is still enabled and you need to verify the changes.

Here is a command to verify common ports when using the Zimbra proxy (run this at the proxy):

for p in 993 995 443 ; do echo Port $p ; timeout 3 openssl s_client -connect `zmhostname`:$p -ssl3 |grep failure ; done

If you are proxying adminUI, please add port 9071, 7071 or the port you have configured. If you are proxying SSO requests, please add port 3443.

List of ports: 443 - HTTPS 993 - IMAP-SSL 995 - POP3-SSL 9071 - AdminUI SSL

For Postfix, run the following command at the MTA for the SMTP-SSL port (465):

timeout 3 openssl s_client -connect `zmhostname`:465 -ssl3
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