CVE-2017-2669
Dovecot before version 2.2.29 is vulnerable to a denial of service. When โdictโ 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.
Source: CVE-2017-2669