High 7.5Published Sep 1, 2026

CVE-2026-84145Internally found bugs fixed in Thunderbird 155, Thunderbird ESR 153.2 and Thunderbird ESR 140.15

Updated under an hour ago (Oct 26, 2026, 6:10 PM ET)

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It affects Mozilla Firefox and 1 other product. Add what you run to find out whether that includes you.

No exploitation reported and no EPSS estimate yet.

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Exploited in the last 30 days

Internally found bugs present in Thunderbird 154, Thunderbird ESR 153.1 and Thunderbird ESR 140.14. Some of these bugs showed evidence of memory corruption or another security-relevant defect and we presume that with enough effort some of these could have been exploited. This vulnerability was fixed in Firefox 155, Firefox ESR 115.40, Firefox ESR 140.15, Firefox ESR 153.2, Thunderbird 155, Thunderbird 140.15, and Thunderbird 153.2.

CVSS: 7.5 HIGH (v3.1, CISA ADP)CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:H/I:H/A:H
Weakness (CWE): CWE-119
Known exploited: Not in CISA's KEV catalog
EPSS (exploitation in the next 30 days): Not loaded for this CVE
Assigned by: mozilla
NVD analysis: Analyzed
Record last updated: Sep 1, 2026
First seen by InfoSec Signals: Oct 9, 2026

Affected products

Affected products

Mozilla Firefox mozilla:firefox (from the name)	115.40 builds before 115.* not affected; 140.15 builds before 140.* not affected; 153.2 builds before 153.* not affected; from 155 not affected	CNA record
Mozilla Thunderbird mozilla:thunderbird (from the name)	140.15 builds before 140.* not affected; 153.2 builds before 153.* not affected; from 155 not affected	CNA record
mozilla firefox mozilla:firefox	before 115.40.0; from 116.0 before 140.15.0; from 141.0.0 before 153.2.0; from 154.0.0 before 155.0.0	NVD
mozilla thunderbird mozilla:thunderbird	before 140.15.0; from 141.0 before 153.2.0; from 154.0 before 155.0	NVD

References

References

https://bugzilla.mozilla.org/buglist.cgi?bug_id=2054640%2C2054650%2C2054652%2C2055693%2C2055705%2C2058051%2C2058652%2C2058660%2C2059027%2C2061220%2C2061242%2C2061285%2C2061300%2C2061316%2C2061397	broken-link
https://bugzilla.mozilla.org/buglist.cgi?bug_id=2058001%2C2059139%2C2062400%2C2062419	broken-link
https://bugzilla.mozilla.org/show_bug.cgi?id=2055678	permissions-required
https://www.mozilla.org/security/advisories/mfsa2026-82/	vendor-advisory
https://www.mozilla.org/security/advisories/mfsa2026-83/	vendor-advisory
https://www.mozilla.org/security/advisories/mfsa2026-84/	vendor-advisory
https://www.mozilla.org/security/advisories/mfsa2026-85/	vendor-advisory
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

The CVE record on cve.org NVD's entry

The CVE record is authoritative. Products marked “from the name” were identified from the CNA's free-text names, not a CPE, and are matched less certainly. This product uses the NVD API but is not endorsed or certified by the NVD.