FreeBSD: VID-a8c8001b-216c-11e7-80aa-005056925db4 (CVE-2017-2669): dovecot -- Dovecot DoS when passdb dict was used for authentication

Dovecot before version 2.2.29 is vulnerable to a denial of service. When 'dict' passdb and userdb were used for user authentication, the username sent by the IMAP/POP3 client was sent through var_expand() to perform %variable expansion. Sending specially crafted %variable fields could result in excessive memory usage causing the process to crash (and restart), or excessive CPU usage causing all authentications to hang.