Vulnerability · NVD

CVE-2026-84143

CVE-2026-84143, critical severity (CVSS 9.8): 2 tracked apps concerned, all fixed or indeterminable on their current version.

Severity (CVSS): 9.8
Exploitation: 0.2 %
Tracked apps: 2
Still exposed: 0

Published on 2026-09-01

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 140.15, Firefox ESR 153.2, Thunderbird 155, Thunderbird 140.15, and Thunderbird 153.2.

Attack vector : Network No privileges required No user interaction

Show raw CVSS vector

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

EPSS 0.17% exploit very unlikely percentile 6.2%

Tracked apps referencing this CVE

For each app: the affected range, the fixing version, and where the tracked app stands today.

Mozilla Firefox Windows winget:Mozilla.Firefox

Affected <140.15.0 Fixed in 140.15.0 Latest tracked 155.0 patched

Observed affected builds (127)

140.0.4 140.0.2 140.0.1 140.0 139.0.4 139.0.1 139.0 138.0.4 138.0.3 138.0.1 138.0 137.0.2 137.0.1 137.0 136.0.4 136.0.3 136.0.2 136.0.1 136.0 135.0.1 135.0 134.0.2 134.0.1 134.0 133.0.3 133.0 132.0.2 132.0.1 132.0 131.0.3 +97 · see history
Mozilla Thunderbird Windows winget:Mozilla.Thunderbird

Affected <140.15.0 Fixed in 140.15.0 Latest tracked 155.0 patched

Observed affected builds (100)

140.0.1 140.0 139.0.2 139.0.1 139.0 138.0.2 138.0.1 138.0 137.0.2 137.0.1 137.0 136.0.1 136.0 115.14.0 115.13.0 115.12.2 115.12.1 115.11.1 115.11.0 115.10.2 115.10.1 115.10.0 115.9.0 115.8.1 115.8.0 115.7.0 115.6.1 115.6.0 115.5.2 115.5.1 +70 · see history

Vulnerable CPE configurations (6)

Vendor	Product	Platform	Versions	CPE 2.3 URI
mozilla	firefox All platforms (wildcard)	All platforms (wildcard)	<140.15.0	cpe:2.3:a:mozilla:firefox::::::::
mozilla	firefox All platforms (wildcard)	All platforms (wildcard)	≥141.0.0 <153.2.0	cpe:2.3:a:mozilla:firefox::::::::
mozilla	firefox All platforms (wildcard)	All platforms (wildcard)	≥154.0.0 <155.0.0	cpe:2.3:a:mozilla:firefox::::::::
mozilla	thunderbird All platforms (wildcard)	All platforms (wildcard)	<140.15.0	cpe:2.3:a:mozilla:thunderbird::::::::
mozilla	thunderbird All platforms (wildcard)	All platforms (wildcard)	≥141.0 <153.2.0	cpe:2.3:a:mozilla:thunderbird::::::::
mozilla	thunderbird All platforms (wildcard)	All platforms (wildcard)	≥154.0 <155.0	cpe:2.3:a:mozilla:thunderbird::::::::

View on NVD ↗ Advisory · www.mozilla.org