Mutt 1.5.19, when linked against (1) OpenSSL (mutt_ssl.c) or (2) GnuTLS (mutt_ssl_gnutls.c), allows connections when only one TLS certificate in the chain is accepted instead of verifying the entire chain, which allows remote attackers to spoof trusted servers via a man-in-the-middle attack.
https://www.redhat.com/archives/fedora-package-announce/2009-June/msg00715.html
https://exchange.xforce.ibmcloud.com/vulnerabilities/51068