See http://www.securityfocus.com/vdb/bottom.html?vid=1110

From the discussion there:

A buffer overflow exists in imapd4r1 version 12.264. The vulnerability
exists in the list command. By supplying a long, well crafted buffer as the
second argument to the list command, it becomes possible to execute code on
the machine.

Executing the list command requires an account on the machine. In addition,
privileges have been dropped in imapd prior to the location of the buffer
overrun. As such, this vulnerability would only be useful in a scenario
where a user has an account, but no shell level access. This would allow
them to gain shell access.

This version of imapd is the one shipped with RedHat Linux 6.2.