thunderbird is vulnerable to remote code execution. During the plaintext phase of the STARTTLS connection setup, protocol commands could have been injected and evaluated within the encrypted session.
access.redhat.com/errata/RHSA-2021:0299
access.redhat.com/security/updates/classification/#important
bugzilla.mozilla.org/show_bug.cgi?id=1622640
bugzilla.redhat.com/show_bug.cgi?id=1921543
www.mozilla.org/en-US/security/advisories/mfsa2021-05/#CVE-2020-15685
www.mozilla.org/security/advisories/mfsa2021-05/