Buffer overflow in copy.c in Mutt before 1.5.23 allows remote attackers to cause a denial of service (crash) via a crafted RFC2047 header line, related to address expansion.
Mutt does not verify that the smtps server hostname matches the domain name of the subject of an X.509 certificate, which allows man-in-the-middle attackers to spoof an SSL SMTP server via an arbitrary certificate, a different vulnerability than CVE-2009-3766.