Exim is a Message Transfer Agent (MTA) developed at the University of Cambridge for Unix based systems.

It is extremely important to keep your Mail Server Security settings in check and the first step is making sure your MTA is up to date.

As of 10th December 2010 a nasty root access exploit has been published which exploits a vulnerability present in Exim versions 4.69 and earlier.

You can view a cPanel advisory regarding this exploit here:

http://www.cpanel.net/2010/12/exim-remote-memory-corruption-vulnerability-notification-cve-2010-4344.html

In order to see which version of Exim your server is running:

rpm -qa | grep exim

As cPanel keeps its own release tree for Exim, you can upgrade by performing the following via SSH:

/scripts/eximup

or to force a reinstall:

/scripts/eximup –force

If you are not running cPanel/WHM, consult the relevant documentation & release advisories for your Linux distribution.