expand.c in Exim before 4.83 expands mathematical comparisons twice, which allows local users to gain privileges and execute arbitrary commands via a crafted lookup value.
http://lists.fedoraproject.org/pipermail/package-announce/2014-August/136251.html
http://lists.fedoraproject.org/pipermail/package-announce/2014-August/136264.html
https://bugzilla.redhat.com/show_bug.cgi?id=1122552