CVE-2026-5731

  1. OpenCVE
  2. Vulnerabilities (CVE)
  3. CVE-2026-5731
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.

9.8 /10

CVSS v3 : CRITICAL

V3 Legend

Vector :

Exploitability : 3.9 / Impact : 5.9

Attack Vector NETWORK

Attack Complexity LOW

Privileges Required NONE

User Interaction NONE

Confidentiality Impact HIGH

Integrity Impact HIGH

Availability Impact HIGH

Scope UNCHANGED

References
Link Resource
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 Broken Link
https://www.mozilla.org/security/advisories/mfsa2026-25/ Vendor Advisory
https://www.mozilla.org/security/advisories/mfsa2026-26/ Vendor Advisory
https://www.mozilla.org/security/advisories/mfsa2026-27/ Vendor Advisory
https://www.mozilla.org/security/advisories/mfsa2026-28/ Vendor Advisory
https://www.mozilla.org/security/advisories/mfsa2026-29/ Vendor Advisory
Configurations

Configuration 1 (hide)

OR cpe:2.3:a:mozilla:firefox:115.34.0:*:*:*:esr:*:*:*
cpe:2.3:a:mozilla:firefox:140.9.0:*:*:*:esr:*:*:*
cpe:2.3:a:mozilla:firefox:149.0.1:*:*:*:-:*:*:*
cpe:2.3:a:mozilla:thunderbird:140.9.0:*:*:*:esr:*:*:*
cpe:2.3:a:mozilla:thunderbird:149.0.1:*:*:*:-:*:*:*
History

16 Apr 2026, 18:59

Type Values Removed Values Added
CPE cpe:2.3:a:mozilla:thunderbird:149.0.1:*:*:*:-:*:*:*
cpe:2.3:a:mozilla:firefox:115.34.0:*:*:*:esr:*:*:*
cpe:2.3:a:mozilla:firefox:140.9.0:*:*:*:esr:*:*:*
cpe:2.3:a:mozilla:thunderbird:140.9.0:*:*:*:esr:*:*:*
cpe:2.3:a:mozilla:firefox:149.0.1:*:*:*:-:*:*:*
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 - () 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 - Broken Link
References () https://www.mozilla.org/security/advisories/mfsa2026-25/ - () https://www.mozilla.org/security/advisories/mfsa2026-25/ - Vendor Advisory
References () https://www.mozilla.org/security/advisories/mfsa2026-26/ - () https://www.mozilla.org/security/advisories/mfsa2026-26/ - Vendor Advisory
References () https://www.mozilla.org/security/advisories/mfsa2026-27/ - () https://www.mozilla.org/security/advisories/mfsa2026-27/ - Vendor Advisory
References () https://www.mozilla.org/security/advisories/mfsa2026-28/ - () https://www.mozilla.org/security/advisories/mfsa2026-28/ - Vendor Advisory
References () https://www.mozilla.org/security/advisories/mfsa2026-29/ - () https://www.mozilla.org/security/advisories/mfsa2026-29/ - Vendor Advisory
First Time Mozilla
Mozilla firefox
Mozilla thunderbird

13 Apr 2026, 15:17

Type Values Removed Values Added
Summary (en) 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 affects Firefox < 149.0.2, Firefox ESR < 115.34.1, Firefox ESR < 140.9.1, Thunderbird < 149.0.2, and Thunderbird < 140.9.1. (en) 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.

07 Apr 2026, 19:16

Type Values Removed Values Added
Summary (en) 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 affects Firefox < 149.0.2, Firefox ESR < 115.34.1, and Firefox ESR < 140.9.1. (en) 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 affects Firefox < 149.0.2, Firefox ESR < 115.34.1, Firefox ESR < 140.9.1, Thunderbird < 149.0.2, and Thunderbird < 140.9.1.
References
  • () https://www.mozilla.org/security/advisories/mfsa2026-28/ -
  • () https://www.mozilla.org/security/advisories/mfsa2026-29/ -

07 Apr 2026, 15:17

Type Values Removed Values Added
CVSS v2 : unknown
v3 : unknown 		v2 : unknown
v3 : 9.8
CWE CWE-119

07 Apr 2026, 13:16

Type Values Removed Values Added
New CVE
Information

Published : 2026-04-07 13:16

Updated : 2026-04-16 18:59

NVD link : CVE-2026-5731

Mitre link : CVE-2026-5731

CVE.ORG link : CVE-2026-5731

JSON object : View

Products Affected

mozilla

  • firefox
  • thunderbird
CWE
CWE-119

Improper Restriction of Operations within the Bounds of a Memory Buffer