Mutt 1.11.0 through 2.0.x before 2.0.7 (and NeoMutt 2019-10-25 through 2021-05-04) has a $imap_qresync issue in which imap/util.c has an out-of-bounds read in situations where an IMAP sequence set ends with a comma. NOTE: the $imap_qresync setting for QRESYNC is not enabled by default.
rfc822.c in Mutt through 2.0.4 allows remote attackers to cause a denial of service (mailbox unavailability) by sending email messages with sequences of semicolon characters in RFC822 address fields (aka terminators of empty groups). A small email message from the attacker can cause large memory consumption, and the victim may then be unable to see email messages from other persons.
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.