How to disable SSLv3

Revision as of 00:37, 17 October 2014 by Plobbes (talk | contribs) (Testing: - show an example of openssl output when SSLv3 is disabled on Jetty)

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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 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.

Warnings:

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.

Postfix (MTA)

Warnings:

  • The current 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. This vector does not apply to non-HTTPS scenarios without using a browser. So right now the risk of exploiting this vulnerability with SMTP is low but we are including here information on how to disable SSLv3 for Postfix (MTA).
  • 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'
postconf -e smtpd_tls_mandatory_protocols='!SSLv2,!SSLv3'

Run "zmmtactl stop ; zmmtactl start" to force the changes on zimbraMtaSmtpdTlsProtocols or wait for mailboxd to rewrite Postfix config from LDAP after 2 minutes. Note that smtpd_tls_mandatory_protocols will need to be set after every upgrade as there is no way to preserve them for now in 8.5.x versions.

ZCS 8.0.x

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 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:

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.pop3s.default.template
nginx.conf.mail.pop3s.template
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

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

We have provided downloadable /opt/zimbra/jetty/etc/jetty.xml.in file locations for IRONMAIDEN. 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

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
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