Vulnerability · NVD

CVE-2026-84639

CVE-2026-84639, critical severity (CVSS 9.1): 1 tracked app concerned, all fixed or indeterminable on their current version.

Severity (CVSS): 9.1
Exploitation: 0.2 %
Tracked apps: 1
Still exposed: 0

Published on 2026-09-01

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.

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:N/A:H

EPSS 0.15% exploit very unlikely percentile 4.5%

Tracked apps referencing this CVE

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

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 (3)

Vendor	Product	Platform	Versions	CPE 2.3 URI
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