* CVE-2019-3814: If imap/pop3/managesieve/submission client has
trusted certificate with missing username field
(ssl_cert_username_field), under some configurations Dovecot
mistakenly trusts the username provided via authentication instead
of failing.
* ssl_cert_username_field setting was ignored with external SMTP AUTH,
because none of the MTAs (Postfix, Exim) currently send the
cert_username field. This may have allowed users with trusted
certificate to specify any username in the authentication. This bug
didn't affect Dovecot's Submission service.
PR: 235523
Submitted by: pascal.christen@hostpoint.ch
MFH: 2019Q1
Security: 1340fcc1-2953-11e9-bc44-a4badb296695
Security: CVE-2019-3814
a434efa6bf