CVE-2026-5731

CRITICAL

Memory safety bugs fixed in Firefox ESR 115.34.1, Firefox ESR 140.9.1, Thunderbird ESR 140.9.1, Firefox 149.0.2 and Thunderbird 149.0.2

Title source: cna

Description

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.

References (6)

https://bugzilla.mozilla.org/buglist.cgi?bug_id=2021894%2C2022225%2C2022252%2C2022294%2C2023007%2C2023130%2C2023191%2C2023364%2C2023829%2C2024074%2C2024417%2C2024433%2C2024436%2C2024437%2C2024453%2C2024461%2C2024462%2C2024472%2C2024474%2C2024477%2C2025364%2C2025401%2C2025402%2C2025472%2C2026287%2C2026299%2C2026305%2C2026426

https://www.mozilla.org/security/advisories/mfsa2026-25/

https://www.mozilla.org/security/advisories/mfsa2026-26/

https://www.mozilla.org/security/advisories/mfsa2026-27/

https://www.mozilla.org/security/advisories/mfsa2026-28/

https://www.mozilla.org/security/advisories/mfsa2026-29/

Scores

CVSS v3 9.8

EPSS 0.0006

EPSS Percentile 20.0%

Attack Vector NETWORK

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

CISA SSVC

Vulnrichment

Exploitation none

Automatable no

Technical Impact total

Details

CWE

CWE-119

Status published

Products (15)

mozilla/firefox 115.34.0

mozilla/firefox 140.9.0

mozilla/firefox 149.0.1

Mozilla/Firefox 115.34.1 - 115.*

Mozilla/Firefox 140.9.1 - 140.*

Mozilla/Firefox 149.0.2

Mozilla/Firefox unspecified - 149.0.2

Mozilla/Firefox ESR unspecified - 115.34.1

Mozilla/Firefox ESR unspecified - 140.9.1

mozilla/thunderbird 140.9.0

... and 5 more

Published Apr 07, 2026

Tracked Since Apr 07, 2026