CVE-2026-84641
A malicious IMAP server can trigger use-after-free and heap-memory disclosure by sending a crafted ID response. Heap contents can ultimately be persisted to prefs.js. 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