Exim 3.22 and earlier, in some configurations, does not properly verify the local part of an address when redirecting the address to a pipe, which could allow remote attackers to execute arbitrary commands via shell metacharacters.
https://exchange.xforce.ibmcloud.com/vulnerabilities/7738
http://www.securityfocus.com/bid/3728
http://www.redhat.com/support/errata/RHSA-2001-176.html
http://www.kb.cert.org/vuls/id/283723