How to disable SSLv3
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This article applies to the following ZCS versions. |
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 https://bugzilla.zimbra.com/show_bug.cgi?id=95976 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)
8.5.x
zmprov mcf zimbraMtaSmtpdTlsProtocols '!SSLv2,!SSLv3'
8.0.x
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.
Nginx (Proxy)
8.5.x
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;
Example:
# HTTPS Proxy Default Configuration # server { 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:
Example: # POP3S proxy default configuration # server { ssl_protocols TLSv1 TLSv1.1 TLSv1.2; [...]
Restart the proxy servers with: "zmproxyctl stop ; zmproxyctl start"
Jetty (mailboxd)
Verifying
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