CVE-2026-84639
CRITICALCVSS 9.1/10EPSS 0.34%
Last modified
CVE-2026-84639 is a critical-severity vulnerability rated 9.1/10 on the CVSS scale. 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.. EPSS estimates a 0.34% chance of exploitation in the next 30 days.
Description
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.
Metrics
Weakness Enumeration
Affected Software
| Vendor | Product | Versions |
|---|---|---|
| Mozilla | Thunderbird | < 140.15.0 |
| Mozilla | Thunderbird | >= 141.0, < 153.2.0 |
| Mozilla | Thunderbird | >= 154.0, < 155.0 |
References
- https://bugzilla.mozilla.org/show_bug.cgi?id=2061087Permissions Required
- https://www.mozilla.org/security/advisories/mfsa2026-86/Vendor Advisory
- https://www.mozilla.org/security/advisories/mfsa2026-87/Vendor Advisory
- https://www.mozilla.org/security/advisories/mfsa2026-88/Vendor Advisory
Timeline
- Published
- Last Modified
- Status
- Analyzed
Frequently Asked Questions
What is 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.
How severe is CVE-2026-84639?
CVE-2026-84639 has a CVSS score of 9.1/10 (CRITICAL severity). The EPSS model estimates a 0.34% probability of exploitation in the next 30 days.
How do I fix CVE-2026-84639?
Check the vendor references and advisories linked above for patched versions and mitigation guidance. You can also run a Strix scan to test if your systems are affected.
How Strix Helps
- How Strix found a critical auth bypass in etcdStrix autonomously discovered a critical authentication bypass in etcd, later designated CVE-2026-33413.
- Autonomous PentestingAI agents that find and validate exploitable vulnerabilities like this one across your applications.
- PR ReviewsPentest every pull request so vulnerable code is caught before it ships to production.
- AI Penetration TestingHow AI-driven penetration testing continuously covers your attack surface.
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Are you affected by CVE-2026-84639?
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