Vulnerability record · CVE-2026-84641 · published 1 September 2026

CVE-2026-84641: Mozilla thunderbird use after free vulnerability

Mozilla · Thunderbird

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.

7.5 CVSS 3.1 High EPSS 0.27% · top 83.1% CWE-416 · Use after free

7.5CVSS 3.1 base score

0.27%EPSS exploitation probability, 30 days

NoNot in CISA KEV

1Affected product versions listed by NVD

4References

3 Sep 2026Last modified by NVD

Description

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

Affected products

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

Thunderbird Mozilla

References

Link	Tags
https://bugzilla.mozilla.org/show_bug.cgi?id=2057805	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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Related vulnerabilities

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

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Source: NIST National Vulnerability Database (record CVE-2026-84641), CISA KEV, FIRST EPSS (scores of 2026-09-26). This page is refreshed as NVD updates the record.