The signature of a digitally signed S/MIME email message may optionally specify the signature creation date and time. If present, Thunderbird did not compare the signature creation date with the message date and time, and displayed a valid signature despite a date or time mismatch. This could be used to give recipients the impression that a message was sent at a different date or time. This vulnerability affects Thunderbird < 115.6.

References

• https://nvd.nist.gov/vuln/detail/CVE-2023-50761
• https://bugzilla.mozilla.org/show_bug.cgi?id=1865647
• https://www.mozilla.org/security/advisories/mfsa2023-55/
• https://www.debian.org/security/2023/dsa-5582
• https://lists.debian.org/debian-lts-announce/2023/12/msg00021.html