plugins/acl/acl-backend-vfile.c in Dovecot 1.2.x before 1.2.15 and 2.0.x before 2.0.5 interprets an ACL entry as a directive to add to the permissions granted by another ACL entry, instead of a directive to replace the permissions granted by another ACL entry, in certain circumstances involving the private namespace of a user, which allows remote authenticated users to bypass intended access restrictions via a request to read or modify a mailbox.
lists.opensuse.org/opensuse-security-announce/2010-11/msg00001.html
marc.info/?l=oss-security&m=128620520732377&w=2
marc.info/?l=oss-security&m=128622064325688&w=2
secunia.com/advisories/43220
www.dovecot.org/list/dovecot/2010-October/053450.html
www.dovecot.org/list/dovecot/2010-October/053451.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/2010/2572
www.vupen.com/english/advisories/2010/2840
www.vupen.com/english/advisories/2011/0301