How to disable SSLv3
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How to disable SSLv3
Last Update: 17:30, 03 November 2014 (UTC)
Due to the recent discovery of a new SSLv3 vulnerability (CVE-2014-3566: Poodle SSLv3), this protocol has been considered unsafe. This is a protocol flaw and Zimbra will 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 helps show how to disable SSLv3 in Zimbra where possible. This has been tested on both ZCS 8.0.8 and 8.5.0 releases.
Warnings:
- The published attack vector as shown by the researchers works with controlling the plaintext sent to the server using Javascript being run on the victim's machine. Attacks via other vectors exist with varying levels of difficulty, and the use of SSLv3 will be deprecated in a future version of ZCS. This document includes information on how to disable SSLv3 for Postfix (MTA), nginx (POP3-SSL and IMAP-SSL) for customers want to do this now. At the moment, it's not possible to disable SSLv3 with mailboxd (Jetty) for POP3-SSL and IMAP-SSL (this will be fixed in 8.6.0, ref https://bugzilla.zimbra.com/show_bug.cgi?id=96040). Bug https://bugzilla.zimbra.com/show_bug.cgi?id=96041 is tracking the deprecation of SSLv3 in ZCS.
- Disabling SSLv3 might prevent older clients/browsers to connect to Zimbra using SSL as they don't support TLS 1.0. Microsoft Internet Explorer 6 on Windows XP or earlier is known to to require SSLv3 (it does not support TLS1.0, TLS1.1 or TLS1.2): https://en.wikipedia.org/wiki/Transport_Layer_Security#Web_browsers
- There may be issues with "Windows Phone 7" [1] requiring SSLv3 (unconfirmed). Most users should already be on Windows Phone 8, as Windows Phone 7 was EOL'd by Microsoft on Oct 14, 2014.
- Disabling SSLv3 for POP3-SSL and IMAP-SSL through nginx might prevent a few clients to connect to Zimbra. Windows Phone 7 users are known to have this issue. This affects users using the Nokia Lumia 710 and Lumia 800 devices.
- Using TLS_ECDHE_RSA_WITH_AES_256_CBC_SHA with zimbraSSLExcludeCipherSuites prevents saslauthd (through libcurl) to work properly when it defaults back to TLS. This affects smtpd authentication via zmauth. Please remove it from your list of excluded ciphers with: zmprov mcf -zimbraSSLExcludeCipherSuites TLS_ECDHE_RSA_WITH_AES_256_CBC_SHA
Recommendation:
- For multi-server installations where only your proxy/MTAs will be exposed do the Internet, it should be enough to only disable SSLv3 at these hosts.
Nginx (Proxy)
ZCS 8.0.x / 8.5.x
Tarballs of the SSL specific Nginx configuration template files have been provided which disables SSLv3 for HTTPS/IMAPS/POP3S. Please make a backup of /opt/zimbra/conf/nginx/templates prior to proceeding.
ZCS 8.0.x http://files.zimbra.com/downloads/support/bug95976/nginx/nginx-ssl-templates-80x.tgz
ZCS 8.5.0 http://files.zimbra.com/downloads/support/bug95976/nginx/nginx-ssl-templates-850.tgz
Installation is the same for both ZCS 8.0.x and 8.5.0, just be sure to download the correct tarball for your ZCS version. To install as root
cd /opt/zimbra/conf/nginx/templates curl http://files.zimbra.com/downloads/support/bug95976/nginx/nginx-ssl-templates-80x.tgz | tar zxvf - su - zimbra zmproxyctl restart
Alternatively, you can edit each nginx template file separately. For all nginx templates in /opt/zimbra/conf/nginx/templates/ that use SSL, set the ssl_protocols option:
/opt/zimbra/conf/nginx/templates/:
nginx.conf.mail.imaps.default.template nginx.conf.mail.imaps.template nginx.conf.mail.imap.default.template (for starttls) nginx.conf.mail.imap.template (for starttls) nginx.conf.mail.pop3s.default.template nginx.conf.mail.pop3s.template nginx.conf.mail.pop3.default.template (for starttls) nginx.conf.mail.pop3.template (for starttls) nginx.conf.mail.template nginx.conf.web.admin.default.template nginx.conf.web.admin.template nginx.conf.web.https.default.template nginx.conf.web.https.template nginx.conf.web.sso.default.template nginx.conf.web.sso.template
For example, you will see an "ssl" block in each of these within the server { } section:
ssl on;
ssl_prefer_server_ciphers ${web.ssl.preferserverciphers};
ssl_ciphers ${web.ssl.ciphers};
ssl_certificate ${ssl.crt.default};
ssl_certificate_key ${ssl.key.default};
Add the following to the end of the ssl section:
ssl_protocols TLSv1 TLSv1.1 TLSv1.2;
The result will look something like this (may vary per file):
server
{
${core.ipboth.enabled}listen [::]:${web.https.port} default;
${core.ipv4only.enabled}listen ${web.https.port} default;
${core.ipv6only.enabled}listen [::]:${web.https.port} default ipv6only=on;
server_name ${web.server_name.default}.default;
client_max_body_size 0;
ssl on;
ssl_prefer_server_ciphers ${web.ssl.preferserverciphers};
ssl_ciphers ${web.ssl.ciphers};
ssl_certificate ${ssl.crt.default};
ssl_certificate_key ${ssl.key.default};
ssl_protocols TLSv1 TLSv1.1 TLSv1.2;
...
Restart the proxy servers with the following:
zmproxyctl restart
ZCS 7.x.y
Disabling SSlv3 for ZCS 7 must be performed manually, and is only available for the nginx proxy and postfix. General recommendation is to use the nginx proxy on all ZCS sites, even single-server platform.
For all nginx templates in /opt/zimbra/conf/nginx/templates/ that use SSL, set the ssl_protocols option:
/opt/zimbra/conf/nginx/templates/:
nginx.conf.mail.imaps.default.template nginx.conf.mail.imaps.template nginx.conf.mail.imap.default.template (for starttls) nginx.conf.mail.imap.template (for starttls) nginx.conf.mail.pop3s.default.template nginx.conf.mail.pop3s.template nginx.conf.mail.pop3.default.template (for starttls) nginx.conf.mail.pop3.template (for starttls) nginx.conf.mail.template nginx.conf.web.https.default.template nginx.conf.web.https.template nginx.conf.web.sso.default.template nginx.conf.web.sso.template
For example, you will see an "ssl" block in each of these within the server { } section:
ssl on;
ssl_prefer_server_ciphers ${web.ssl.preferserverciphers};
ssl_ciphers ${web.ssl.ciphers};
ssl_certificate ${ssl.crt.default};
ssl_certificate_key ${ssl.key.default};
Note that nginx 0.9 is used in ZCS 7, so only the ssl_protocols option "TLSv1" is available. Add the following to the end of the ssl section:
ssl_protocols TLSv1;
The result will look something like this (may vary per file):
server
{
${core.ipboth.enabled}listen [::]:${web.https.port} default;
${core.ipv4only.enabled}listen ${web.https.port} default;
${core.ipv6only.enabled}listen [::]:${web.https.port} default ipv6only=on;
server_name ${web.server_name.default}.default;
client_max_body_size 0;
ssl on;
ssl_prefer_server_ciphers ${web.ssl.preferserverciphers};
ssl_ciphers ${web.ssl.ciphers};
ssl_certificate ${ssl.crt.default};
ssl_certificate_key ${ssl.key.default};
ssl_protocols TLSv1;
...
Restart the proxy servers with the following:
zmproxyctl restart
Testing
You can run the following 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 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.
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.
In alternative, you can test the following ports individually:
443 - HTTPS 993 - IMAP-SSL 995 - POP3-SSL 9071 or 7071 - AdminUI SSL
with
openssl s_client -connect host.zimbra.com:<port> -ssl3
Jetty (mailboxd)
ZCS 8.0.x
- Note: at the moment, it's not possible to disable SSLv3 with mailboxd (Jetty) for POP3-SSL and IMAP-SSL. These templates only disable SSLv3 on https (443 and 7071).
We have provided downloadable /opt/zimbra/jetty/etc/jetty.xml.in file locations for ZCS 8.0.x. Make sure you backup the original jetty.xml.in first.
ZCS 8.0.0-8.0.2 http://files.zimbra.com/downloads/support/bug95976/jetty/800-802/jetty.xml.in
ZCS 8.0.3 http://files.zimbra.com/downloads/support/bug95976/jetty/803/jetty.xml.in
ZCS 8.0.4-8.0.6 http://files.zimbra.com/downloads/support/bug95976/jetty/804-806/jetty.xml.in
ZCS 8.0.7-8.0.8 http://files.zimbra.com/downloads/support/bug95976/jetty/807-808/jetty.xml.in
In alternative you can edit the file and find the SslSelectChannelConnector instances in /opt/zimbra/jetty/etc/jetty.xml.in:
$ grep SslSelectChannel jetty.xml.in
<New id="ssl" class="org.eclipse.jetty.server.ssl.SslSelectChannelConnector">
<New id="ssl-clientcert" class="org.eclipse.jetty.server.ssl.SslSelectChannelConnector">
<New id="admin" class="org.eclipse.jetty.server.ssl.SslSelectChannelConnector">
<New id="admin_local" class="org.eclipse.jetty.server.ssl.SslSelectChannelConnector">
Under each, add the following XML
<Get name="SslContextFactory">
<Set name="ExcludeProtocols">
<Array type="java.lang.String">
<Item>SSLv3</Item>
</Array>
</Set>
</Get>
Don't forget to do a "zmmailboxdctl restart' to apply the changes.
ZCS 8.5.x
- Note: at the moment, it's not possible to disable SSLv3 with mailboxd (Jetty) for POP3-SSL and IMAP-SSL.
Find the SslContextFactory in /opt/zimbra/jetty/etc/jetty.xml.in and add this XML:
<Set name="ExcludeProtocols">
<Array type="java.lang.String">
<Item>SSLv3</Item>
</Array>
</Set>
Do a "zmmailboxdctl restart' to apply the changes.
Testing
We should run the following command (as zimbra) for every port using SSL:
openssl s_client -connect `zmhostname`:<port> -ssl3
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:
or below (an example with ZCS 8.0.x and Jetty 7.6 w/SSLv3 successfully disabled):
CONNECTED(00000003)
write:errno=104
---
no peer certificate available
---
No client certificate CA names sent
---
SSL handshake has read 0 bytes and written 0 bytes
---
New, (NONE), Cipher is (NONE)
Secure Renegotiation IS NOT supported
Compression: NONE
Expansion: NONE
SSL-Session:
Protocol : SSLv3
Cipher : 0000
Session-ID:
Session-ID-ctx:
Master-Key:
Key-Arg : None
Krb5 Principal: None
PSK identity: None
PSK identity hint: None
Start Time: 1413506064
Timeout : 7200 (sec)
Verify return code: 0 (ok)
---
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.
List of common ports:
443 - HTTPS 993 - IMAP-SSL 995 - POP3-SSL 7071 - AdminUI SSL
Postfix (MTA)
Warnings:
- Disabling SSLv3 might prevent older mail clients to connect to Zimbra since they might not support TLS. This is important when using the 465 port (SMTP-SSL), where encryption is mandatory (smtpd_tls_mandatory_protocols).
ZCS 8.5.x
At the MTA server, run (as zimbra):
zmprov mcf zimbraMtaSmtpdTlsProtocols '!SSLv2,!SSLv3'
Run "zmmtactl stop ; zmmtactl start" to force the changes on zimbraMtaSmtpdTlsProtocols or wait for zmconfigd to rewrite Postfix config from LDAP in 1 minute or less.
ZCS 8.0.x and ZCS 7.x.y
At the MTA server, run (as zimbra):
postconf -e smtpd_tls_protocols='!SSLv2,!SSLv3' postconf -e smtpd_tls_mandatory_protocols='!SSLv2,!SSLv3'
Note that smtpd_tls_protocols and smtpd_tls_mandatory_protocols will need to be set after every upgrade for 8.0.x or 7.x.y versions.
Testing STARTTLS on port 25
Run openssl, forcing SSLv3:
openssl s_client -connect mail.example.com:25 -ssl3 -starttls smtp
Confirm that connection is refused with an "ssl handshake failure":
CONNECTED(00000003) 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 SSL-Session: Protocol : SSLv3 Cipher : 0000 Session-ID: Session-ID-ctx: Master-Key: Key-Arg : None Krb5 Principal: None PSK identity: None PSK identity hint: None Start Time: 1413400965 Timeout : 7200 (sec) Verify return code: 0 (ok)
Testing SMTP-SSL
timeout 3 openssl s_client -connect mail.example.com:465 -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:
