How to obtain an A+ in the Qualys SSL Labs Security Test
Article Information |
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This article applies to the following ZCS versions. |
How to obtain an A+ in the Qualys SSL Labs security test
Purpose
List the steps, per release, to obtain an A+ in the Qualys SSL Labs Security Test.
Resolution
Until have an option in the Admin Console, all of this Wiki is using the CLI.
Zimbra Collaboration 8.7
Work in progress
Zimbra Collaboration 8.6 & 8.5
Fix the Logjam issue
Zimbra 8.6 has per default 1024-bit DH ciphers, as they are secure, the best practice is use at least 2048, and the Qualys SSL Labs test will give us the A+ using the correct ones.
Like root, create a new 2048 key, will take some minutes:
cd /opt/zimbra/conf openssl dhparam -out dhparams.pem 2048 chown zimbra:zimbra dhparams.pem
Edit the next 2 files:
/opt/zimbra/conf/nginx/templates/nginx.conf.web.https.default.template /opt/zimbra/conf/nginx/templates/nginx.conf.web.https.template
You need to add the next content, ssl_dhparam /opt/zimbra/conf/dhparams.pem;, before the include, will looks like:
ssl_verify_client ${ssl.clientcertmode.default}; ssl_verify_depth ${ssl.clientcertdepth.default}; ssl_dhparam /opt/zimbra/conf/dhparams.pem; include ${core.includes}/${core.cprefix}.web.https.mode-${web.mailmode};
Tune the Cipher list
Like zimbra user, run the next command to tune the Ciphers and disable the RC4, etc:
zmprov mcf zimbraReverseProxySSLCiphers '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:AES128-GCM-SHA256:AES256-GCM-SHA384:AES128:AES256:HIGH:!aNULL:!eNULL:!EXPORT:!DES:!MD5:!PSK:!RC4'
Restart the proxy
zmproxyctl restart
Strict Transport Security (HSTS)
Like roor user, edit the next file /opt/zimbra/conf/nginx/templates/nginx.conf.web.https.default.template and add in the section server { the next content :
add_header Strict-Transport-Security "max-age=31536000; includeSubdomains;";
Session resumption (caching)
Like roor user, add the next content after the add_header that you added in the previous step:
ssl_session_cache shared:SSL:50m; ssl_session_timeout 5m;
Then restart the proxy like zimbra user:
zmproxyctl restart
The result
The result in the SSL Labs test will be:
Zimbra Collaboration 8.0.9
Generate a SSL Certiricate with SHA256
Per default, Zimbra Collaboration 8.0.x didn't generate a valid CSR with a 256bit hash. To force it, edit the next file as root:
/opt/zimbra/bin/zmcertmgr
And change this line:
${openssl} req -new -${DIGEST} -nodes -out ${current_csr} -keyout ${current_key} \
For the next one, adding the -sha256 to the OpenSSL command:
${openssl} req -sha256 -new -${DIGEST} -nodes -out ${current_csr} -keyout ${current_key} \
Then you can generate the new CSR, this time with a SHA256, follow the next Wiki.
Fix the Logjam issue
Zimbra Collaboration 8.0.9 can't fix the issue because the DH Cipher keysize is hardcoded in Java 1.7. But like recommendation, you can put a Zimbra Collaboration 8.6 proxy node in front of your environment if you have Single-Server, or if you have Multi-Server you can upgrade, only, your Proxy node to 8.6.
Tune the Cipher list
You will want to disable the RC4, run the nex command:
zmprov modifyConfig +zimbraSSLExcludeCipherSuites TLS_RSA_WITH_RC4_128_MD5 zmprov modifyConfig +zimbraSSLExcludeCipherSuites TLS_RSA_WITH_RC4_128_SHA zmprov modifyConfig +zimbraSSLExcludeCipherSuites SSL_RSA_WITH_RC4_128_MD5 zmprov modifyConfig +zimbraSSLExcludeCipherSuites SSL_RSA_WITH_RC4_128_SHA zmprov modifyConfig +zimbraSSLExcludeCipherSuites TLS_ECDHE_RSA_WITH_RC4_128_SHA zmcontrol restart
Disable SSLv3 to fix the Poodle
Follow the next Wiki to disable SSLv3 in your Zimbra Collaboration 8.0.x environment.
The result
The result using a valid SSL commercial certificate, and Zimbra Collaboration 8.0.9 Proxy, in the SSL Labs test will be an F, so you need to think to use a Proxy based in 8.6 if you want to keep your environment secure:
Scenario with Single-Server and a Proxy in Zimbra Collaboration 8.6 on front:
Scenario with Multi-Server and a Proxy in Zimbra Collaboration 8.6 on front:
The result of the test without Proxy in 8.6:
Additional Content
- Thank you to http://managedhosting.de for the original wiki about disable logjam - https://wiki.zimbra.com/wiki/Security/Collab/logjam
- Thank you to Irontec to wrote the next Blog entry about how to generate CSR with hash SHA256.