neomutt

In mutt and neomutt, PGP encryption does not use the --hidden-recipient mode which may leak the Bcc email header field by inferring from the recipients info.

In mutt and neomutt the In-Reply-To email header field is not protected by cryptographic signing which allows an attacker to reuse an unencrypted but signed email message to impersonate the original sender.

In neomutt and mutt, the To and Cc email headers are not validated by cryptographic signing which allows an attacker that intercepts a message to change their value and include himself as a one of the recipients to compromise message confidentiality.

Mutt before 2.0.2 and NeoMutt before 2020-11-20 did not ensure that $ssl_force_tls was processed if an IMAP server's initial server response was invalid. The connection was not properly closed, and the code could continue attempting to authenticate. This could result in authentication credentials being exposed on an unencrypted connection, or to a machine-in-the-middle.

Mutt before 1.14.4 and NeoMutt before 2020-06-19 have a STARTTLS buffering issue that affects IMAP, SMTP, and POP3. When a server sends a "begin TLS" response, the client reads additional data (e.g., from a man-in-the-middle attacker) and evaluates it in a TLS context, aka "response injection."