A design flaw in exim4 allowed the loal Debian-exim user to obtain root privileges by specifying an alternate configuration file using the -C option or by using the macro override facility . Unfortunately, fixing this vulnerability is not possible without some changes in exim4"s behvaviour. If you use the -C or -D options or use the system filter facility, you should evaluate the changes carefully and adjust your configuration accordingly. The Debian default configuration is not affected by the changes. The detailed list of changes is described in the NEWS.Debian file in the packages. The relevant sections are also reproduced below. In addition to that, missing error handling for the setuid/setgid system calls allowed the Debian-exim user to cause root to append log data to arbitrary files .