A bug in Exim mailer that was disclosed earlier this week can be used to install a rootkit. US-CERT said the bug already was being exploited in the wild by the time it was disclosed. The bug has been fixed in new version of Exim, which is a mail transfer agent used on Unix-based machines. The rootkit installs itself and creates temporary files to get root access and run a shell as root. The latest version can be downloaded on the Exim site.
Source: https://threatpost.com/rootkit-being-used-attacks-exim-bug-121710/74789/