The OpenConnectionTask::handleStateHelper function in Imap/Tasks/OpenConnectionTask.cpp in Trojita before 0.4.1 allows man-in-the-middle attackers to trigger use of cleartext for saving a message into a (1) sent or (2) draft folder via a PREAUTH response that prevents later use of the STARTTLS command.
The product exposes sensitive information to an actor that is not explicitly authorized to have access to that information.