CVE-2026-84640
A maliciously constructed mail header could lead to a one byte read past the end of a buffer. This vulnerability was fixed in Thunderbird 155, Thunderbird 140.15, and Thunderbird 153.2.
- Published Sep 1, 2026
- CVSS 7.5 high
- 0.3% chance of exploitation in the next 30 days (EPSS)
- A fix is available