Disabling the use of weak DH keys in Zimbra Collaboration mailboxd

Revision as of 17:47, 6 July 2015 by Jorge de la Cruz (talk | contribs) (In the Zimbra Collaboration Server)

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This article applies to the following ZCS versions.

ZCS 7.0 Article ZCS 7.0 ZCS 6.0 Article ZCS 6.0

How to fix Mozilla Firefox error - ssl error weak server ephemeral dh key


Since the 30th of June of 2015, Mozilla Firefox doesn't support connections to a server with weak DH ciphers anymore, as per Mozilla Release Notes:

  • Removed support for insecure SSLv3 for network communications
  • Disable use of RC4 except for temporarily whitelisted hosts

You will see the next error message trying to connect a Zimbra Collaboration 7.x or previous versions:

Secure Connection Failed

An error occurred during a connection to YOUR IP. SSL received a weak ephemeral Diffie-Hellman key in Server Key Exchange handshake message. (Error code: ssl_error_weak_server_ephemeral_dh_key)

* The page you are trying to view cannot be shown because the authenticity of the received data could not be verified.
* Please contact the website owners to inform them of this problem.



You have different steps to resolve the issue:

In the Zimbra Collaboration Server

Disabling the insecure Ciphers, will make Firefox happy again:

zmprov mcf +zimbraSSLExcludeCipherSuites TLS_DHE_RSA_WITH_AES_128_CBC_SHA
zmprov mcf +zimbraSSLExcludeCipherSuites TLS_DHE_RSA_WITH_AES_256_CBC_SHA
zmmailboxdctl restart

You will see the Web Client again:


Upgrade is also a recommended way

The recommended step is upgrade to a Supported Zimbra Collaboration version, 8.x, as Zimbra Collaboration 7.x is EOL since March this year.


If you want to Upgrade, we had an special Webinar that will help you with the process - https://community.zimbra.com/collaboration/f/1884/t/1139230

Mozilla Firefox fix per each client

The second one is disable the new introduced option in Mozilla Firefox, you need to do it in each Web Browser that uses your Zimbra Collaboration Server:

Type about:config in your Firefox web browser, in the address bar. Be careful as you can break your Firefox Configuration easier. Change the next settings with the next values:


Not recommended, enable HTTP & HTTPS

Not recommended, you can set the zmtlsctl to both, to enable HTTP traffic to your server, users will be able to connect using Firefox 39, previous or above versions using HTTP. Like zimbra user:

zmtlsctl both
zmcontrol restart

Additional Content

Verified Against: Zimbra Collaboration 7.x and previous Date Created: 07/06/2015
Article ID: https://wiki.zimbra.com/index.php?title=Disabling_the_use_of_weak_DH_keys_in_Zimbra_Collaboration_mailboxd Date Modified: 2015-07-06

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Wiki/KB reviewed by SME1 SME2 Copyeditor Last edit by Jorge de la Cruz
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