Security Vulnerabilities fixed in Thunderbird 91.13 — Mozilla

An attacker could have abused XSLT error handling to associate attacker-controlled content with another origin which was displayed in the address bar. This could have been used to fool the user into submitting data intended for the spoofed origin.
A cross-origin iframe referencing an XSLT document would inherit the parent domain’s permissions (such as microphone or camera access).
Members the Mozilla Fuzzing Team reported memory safety bugs present in Thunderbird 102.1 and Thunderbird 91.12. Some of these bugs showed evidence of memory corruption and we presume that with enough effort some of these could have been exploited to run arbitrary code.