The remote host is missing an update to kolab-cyrus-imapd announced via advisory DSA 2258-1.

https://secure1.securityspace.com/smysecure/catid.html?in=DSA%202258-1

It was discovered that the STARTTLS implementation of the Kolab 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 2.2.13-5+lenny3. For the stable distribution (squeeze), this problem has been fixed in version 2.2.13-9.1. For the testing distribution (wheezy), this problem has been fixed in version 2.2.13p1-0.1. For the unstable distribution (sid), this problem has been fixed in version 2.2.13p1-0.1. We recommend that you upgrade your kolab-cyrus-imapd packages.