It was discovered that the STARTTLS implementation of the Cyrus IMAP server does not properly restrict I/O buffering, which allows man-in-the-middle attackers to insert commands into encrypted IMAP, LMTP, NNTP and POP3 sessions by sending a cleartext command that is processed after TLS is in place.
For the oldstable distribution (lenny), this problem has been fixed in version 2.2.13-14+lenny4.
For the stable distribution (squeeze), this problem has been fixed in version 2.2.13-19+squeeze1.
For the unstable distribution (sid), this problem has been fixed in version 2.2.13p1-11 for cyrus-imapd-2.2 and in version 2.4.7-1 for cyrus-imapd-2.4.
We recommend that you upgrade your cyrus-imapd-2.2 packages.