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CVE-2026-5731

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

Published: Apr 7, 2026Updated: Jun 30, 2026 Sources: CVE List NVD BDUCWE-119
9.8CRITICAL
NVD MITRE
EPSS Score
0.3%
Top 74.2%
CISA KEV
Not in KEV
Exploits
No Known Exploits
Remediation
Patch Available
Self-Check
OpenVAS

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.

No summary for this CVE yet.

CVSS Vector Breakdown

AV:NAC:LPR:NUI:NS:UC:HI:HA:H
Exploitability
AV:NAttack Vector
Network
AC:LAttack Complexity
Low
PR:NPrivileges Required
None
UI:NUser Interaction
None
Scope
S:UScope
Unchanged
Impact
C:HConfidentiality
High
I:HIntegrity
High
A:HAvailability
High
Open in CVSS calculator →

Weaknesses

CWE-119CWE-787

Affected Products

Mozilla Corp.
oss-project·USaka Mozilla
Firefox ESROn-premDesktop App
Consumer Software / browser
ThunderbirdOn-premDesktop App
Communications / email-server-client
Thunderbird ESR
Consumer Software
АО «ИВК»
commercial·RUaka ivk
АЛЬТ СП 10On-premOS
Operating Systems / linux-distro
and 5 more affected products View all →

Exploitability

Official Patch Available
Is your org exposed to CVE-2026-5731?We can run the check for you — a free external exposure review, no install. Check my exposure

Attack Graph

Products CVE Techniques Tactics

Click technique nodes for MITRE ATT&CK details · drag to pan · Ctrl/⌘ + scroll to zoom, or go fullscreen.

MITRE ATT&CK

2 techniques
Initial Access
Privilege Escalation
View detailed technique mapping

References

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
bugzilla.mozilla.org
https://www.mozilla.org/security/advisories/mfsa2026-25/
mozilla.org
https://www.mozilla.org/security/advisories/mfsa2026-26/
mozilla.org
and 36 more references View all →

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