Mutt before 1.14.3 proceeds with a connection even if, in response to a GnuTLS certificate prompt, the user rejects an expired intermediate certificate.
https://usn.ubuntu.com/4401-1/
https://security.gentoo.org/glsa/202007-57
https://bugs.gentoo.org/728300
http://lists.opensuse.org/opensuse-security-announce/2020-06/msg00070.html
http://lists.opensuse.org/opensuse-security-announce/2020-06/msg00064.html
http://lists.mutt.org/pipermail/mutt-announce/Week-of-Mon-20200608/000022.html