When processing a PGP/MIME payload that contains digitally signed text, the first paragraph of the text was never shown to the user. This is because the text was interpreted as a MIME message and the first paragraph was always treated as an email header section. A digitally signed text from a different context, such as a signed GIT commit, could be used to spoof an email message. This vulnerability affects Thunderbird < 115.6.
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