Vulnerability · NVD

CVE-2026-5731

CVE-2026-5731, critical severity (CVSS 9.8): 2 tracked apps concerned, all fixed or indeterminable on their current version.

Severity (CVSS): 9.8
Exploitation: 0.6 %
Tracked apps: 2
Still exposed: 0

Published on 2026-04-07

Memory safety bugs present in Firefox ESR 115.34.0, Firefox ESR 140.9.0, Thunderbird ESR 140.9.0, Firefox 149.0.1 and Thunderbird 149.0.1. Some of these bugs showed evidence of memory corruption and we presume that with enough effort some of these could have been exploited to run arbitrary code. This vulnerability was fixed in Firefox 149.0.2, Firefox ESR 115.34.1, Firefox ESR 140.9.1, Thunderbird 149.0.2, and Thunderbird 140.9.1.

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 0.61% exploit very unlikely percentile 46.9%

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 - Fixed in - Latest tracked 156.0.1 undetermined
Mozilla Thunderbird Windows winget:Mozilla.Thunderbird

Affected - Fixed in - Latest tracked 156.0.1 undetermined

Vulnerable CPE configurations (5)

Vendor	Product	Platform	Versions	CPE 2.3 URI
mozilla	firefox All platforms (wildcard)	All platforms (wildcard)	-	cpe:2.3:a:mozilla:firefox:115.34.0::::esr:::
mozilla	firefox All platforms (wildcard)	All platforms (wildcard)	-	cpe:2.3:a:mozilla:firefox:140.9.0::::esr:::
mozilla	firefox All platforms (wildcard)	All platforms (wildcard)	-	cpe:2.3:a:mozilla:firefox:149.0.1::::-:::
mozilla	thunderbird All platforms (wildcard)	All platforms (wildcard)	-	cpe:2.3:a:mozilla:thunderbird:140.9.0::::esr:::
mozilla	thunderbird All platforms (wildcard)	All platforms (wildcard)	-	cpe:2.3:a:mozilla:thunderbird:149.0.1::::-:::

View on NVD ↗ Advisory · www.mozilla.org

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