Best Practical Solutions RT 3.8.x before 3.8.15 and 4.0.x before 4.0.8, when GnuPG is enabled with a "Sign by default" queue configuration, uses a queue's key for signing, which might allow remote attackers to spoof messages by leveraging the lack of authentication semantics.
http://lists.bestpractical.com/pipermail/rt-announce/2012-October/000212.html