Security Vulnerabilities fixed in Thunderbird 91.9 — Mozilla

When viewing an email message A, which contains an attached message B, where B is encrypted or digitally signed or both, Thunderbird may show an incorrect encryption or signature status. After opening and viewing the attached message B, when returning to the display of message A, the message A might be shown with the security status of message B.
When reusing existing popups Thunderbird would allow them to cover the fullscreen notification UI, which could enable browser spoofing attacks.
Documents in deeply-nested cross-origin browsing contexts could obtain permissions granted to the top-level origin, bypassing the existing prompt and wrongfully inheriting the top-level permissions.
Thunderbird would behave slightly differently for already known resources, when loading CSS resources through resolving CSS variables. This could be used to probe the browser history.
An improper implementation of the new iframe sandbox keyword allow-top-navigation-by-user-activation could lead to script execution without allow-scripts being present.
Requests initiated through reader mode did not properly omit cookies with a SameSite attribute.
The parent process would not properly check whether the Speech Synthesis feature is enabled, when receiving instructions from a child process.
Mozilla developers Gabriele Svelto, Tom Ritter and the Mozilla Fuzzing Team reported memory safety bugs present in Thunderbird 91.8. 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.