Securing the Kolab Server

This chapter outlines the recommendations for further securing your Kolab Groupware server.


Further securing your Kolab Groupware server may kick you off of mainstream supply channels for further updates possibly including security fixes.

Additionally, it may also not be helpful at all, and provide a false sense of security to you and your users.

Before considering to follow any of the following recommendations, carefully consider the implications of missing a security update because there is not enough time to subscribe, pay attention and follow up.

Your Jurisdiction

Unless you are yourself some or the other form of authority, no level of protection can protect you against the recognized authorities.

Our societies are, in principle, subject to the rule of law – even if that same law allows the authorities to break the law but not break the law [1], and terrorize foreign and domestic populations [2], either with or without reasonable suspicion, with or without disclosure, and/or with or without meaningful judicial review.

Similar legislation may apply to your jurisdiction, but it is not just your own jurisdiction that matters.

Privileged Information in Transit

Some authorities have passed laws that allow them to stop and search otherwise innocent people when in transit through certain areas, seizing materials they may have on them, and detaining the individual for questioning [3].

It is sometimes considered a criminal offence for such individual to not cooperate with the interview(er(s)). So, should a laptop or data carrier you have on you contain privileged information, you may be obliged to disclose your means of protecting that data, or be found uncooperative.

The case for system administrators goes further, as – as a part of their profession – they have access to information that is mostly private, sometimes sensitive, but otherwise still not their own.

You would want to prevent one of your system administrators being forced into the awkward disposition of needing to choose between logging into your systems to retrieve the data requested, and jail.

Using Forward Secrecy

Forward Secrecy, also known as Perfect Forward Secrecy although never actually perfect, uses additional cryptographic measures to prevent a particular TLS session’s key derived from a set of public and private keys is not compromised should one of the private keys be compromised in the future.

The most commonly used ciphers are based on ephemeral Diffie-Hellman (EDH), allowing two parties to anonymously agree upon a shared secret for the session keys, over the not yet secured communication channel.

For a Kolab Groupware environment, Forward Secrecy can be enabled using newer versions of software packages than are otherwise available to mainstream Enterprise Linux distributions.

, but not enforced on all layers of communication;

  • Communications over HTTPS can be secured, but some browsers do not have the required level of encryption capabilities.

  • Communications over IMAP+TLS can be secured, but again depending on the client encryption capabilities, this may or may not include Forward Secrecy.

  • Communications with the MTA/MSA can be secured, but is once more dependent on the client encryption capabilities for the inclusion of Forward Secrecy.

Most of your clients however will have the appropriate capabilities, except for Internet Explorer versions 6 and 8 on Windows XP.

The real problematic area is in communications between your SMTP servers, and those of the rest of the world.

In real life, not many parties purchase an SSL certificate issued by a trusted third party. Additionally, in recent months, it has come to light that most of those trusted third parties can only be trusted as much as the authorities of their domicile and in jurisdictions they operate in.

As such, to accept TLS encryption offered using a self-signed or falsified SSL certificate under the assumption it actually secures anything is a misinformed conclusion. To only accept valid TLS encryption SSL

OpenSSL 1.0.1 or newer

  • When permitted, use the Non-USA version of OpenSSL

  • Enable Ecliptic Curve encryption

Apache httpd 2.4

Apache httpd 2.4 needs to be compiled using _admin-securing_kolab-openssl as described.

SSLEngine On
SSLProtocol all -SSLv2 -SSLv3
SSLHonorCipherOrder on