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Vulnerability record · CVE-2026-84639 · published 1 September 2026

CVE-2026-84639: Mozilla thunderbird vulnerability

Mozilla · Thunderbird

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.

9.1 CVSS 3.1 Critical EPSS 0.32% · top 77.2% CWE-457 · CWE-457
9.1CVSS 3.1 base score
0.32%EPSS exploitation probability, 30 days
NoNot in CISA KEV
1Affected product versions listed by NVD
4References
3 Sep 2026Last modified by NVD

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.

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:H

Affected products

1 vulnerable configurations from NVD's CPE data, grouped by vendor and product.

References

LinkTags
https://bugzilla.mozilla.org/show_bug.cgi?id=2061087 Permissions 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

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Same products first, then exploited flaws of the same weakness class.

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Source: NIST National Vulnerability Database (record CVE-2026-84639), CISA KEV, FIRST EPSS (scores of 2026-09-26). This page is refreshed as NVD updates the record.