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.

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EPSS — Exploit Prediction

0.0032

Probability of exploitation

0.26%

Percentile rank

EPSS estimates the probability that this vulnerability will be exploited in the wild within the next 30 days. A higher score means more likely to be exploited.

References

Other References

https://bugzilla.mozilla.org/show_bug.cgi?id=2061087 https://www.mozilla.org/security/advisories/mfsa2026-86/ https://www.mozilla.org/security/advisories/mfsa2026-87/ https://www.mozilla.org/security/advisories/mfsa2026-88/

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 do I check if I'm vulnerable to CVE-2026-84639? +

You can use Secably's free Website Scanner to check your website for known vulnerabilities. For infrastructure scanning, use the Port Scanner to identify exposed services that may be affected. Check the vendor advisories linked above for specific patch and version information.