CVE-2026-84639
Triggering an error condition in certain MIME bodies would cause uninitialized memory to be used. This vulnerability was fixed in Thunderbird 155, Thunderbird 140.15, and Thunderbird 153.2.
- Published Sep 1, 2026
- CVSS 9.1 critical
- 0.3% chance of exploitation in the next 30 days (EPSS)
- A fix is available