Best Practical Solutions RT 3.8.x before 3.8.15 and 4.0.x before 4.0.8, when GnuPG is enabled, allows remote attackers to configure encryption or signing for certain outbound e-mail, and possibly cause a denial of service (loss of e-mail readability), via an e-mail message to a queue's address.
http://lists.bestpractical.com/pipermail/rt-announce/2012-October/000212.html