Mozilla has published a security advisory, highlighting vulnerabilities in Thunderbird version 78.11 on 3rd June, 2021. It is recommended that you take the necessary precautions by ensuring your products are always updated.
For more information on this Mozilla update, you can follow these URLs:
https://www.mozilla.org/en-US/security/advisories/mfsa2021-26/
The Guyana National CIRT recommends that users and administrators review this update and apply them where necessary.
PDF Download: Mozilla Releases Security Updates for Thunderbird.pdf
References
https://cyber.gc.ca/en/alerts/mozilla-security-advisory-38
https://www.mozilla.org/en-US/security/advisories/mfsa2021-26/