dovecot is vulnerable to denial of service. A flaw was found in the way Dovecot handled SIGCHLD signals. If a large amount of IMAP or POP3 session disconnects caused the Dovecot master process to receive these signals rapidly, it could cause the master process to crash.
secunia.com/advisories/43220
www.dovecot.org/list/dovecot/2010-October/053450.html
www.mandriva.com/security/advisories?name=MDVSA-2010:217
www.redhat.com/support/errata/RHSA-2011-0600.html
www.ubuntu.com/usn/USN-1059-1
www.vupen.com/english/advisories/2010/2840
www.vupen.com/english/advisories/2011/0301
access.redhat.com/errata/RHSA-2011:0600
access.redhat.com/security/updates/classification/#moderate