Dovecot 1.2.x before 1.2.15 and 2.0.x before 2.0.beta2 grants the admin permission to the owner of each mailbox in a non-public namespace, which might allow remote authenticated users to bypass intended access restrictions by changing the ACL of a mailbox, as demonstrated by a symlinked shared mailbox.
secunia.com/advisories/43220
www.dovecot.org/list/dovecot/2010-October/053450.html
www.dovecot.org/list/dovecot/2010-October/053452.html
www.mandriva.com/security/advisories?name=MDVSA-2010:217
www.ubuntu.com/usn/USN-1059-1
www.vupen.com/english/advisories/2010/2840
www.vupen.com/english/advisories/2011/0301