CVE-2026-5731: Vulnerability in Mozilla Firefox
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.
AI Analysis
Technical Summary
CVE-2026-5731 encompasses multiple memory safety bugs affecting Mozilla Firefox and Thunderbird products, specifically in versions Firefox ESR 115.34.0, Firefox ESR 140.9.0, Thunderbird ESR 140.9.0, Firefox 149.0.1, and Thunderbird 149.0.1. These vulnerabilities involve memory corruption issues that could potentially allow an attacker to execute arbitrary code. Mozilla has addressed these issues by releasing patched versions Firefox 149.0.2, Firefox ESR 115.34.1, Firefox ESR 140.9.1, Thunderbird 149.0.2, and Thunderbird 140.9.1. The vulnerabilities are categorized under CWE-119 (Improper Restriction of Operations within the Bounds of a Memory Buffer) and CWE-787 (Out-of-bounds Write). The CVSS v3.1 base score is 9.8, indicating critical severity with network attack vector, low attack complexity, no privileges required, no user interaction, and high impact on confidentiality, integrity, and availability.
Potential Impact
The vulnerabilities could lead to arbitrary code execution due to memory corruption, posing a critical risk to affected systems. Exploitation could compromise confidentiality, integrity, and availability of the affected applications. No known exploits in the wild have been reported at the time of disclosure.
Mitigation Recommendations
Mozilla has released official fixes for these vulnerabilities in Firefox 149.0.2, Firefox ESR 115.34.1, Firefox ESR 140.9.1, Thunderbird 149.0.2, and Thunderbird 140.9.1. Users and administrators should update to these fixed versions immediately to mitigate the risk. Patch status is confirmed by the vendor advisories linked in the report.
CVE-2026-5731: Vulnerability in Mozilla Firefox
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.
CVSS v3.1
Score 9.8critical
Affected software
pkg:github/mozilla/firefoxRun on your own infrastructure? Check whether these packages are installed with threat-finder — our free open-source scanner.
AI-Powered Analysis
Machine-generated threat intelligence
Technical Analysis
CVE-2026-5731 encompasses multiple memory safety bugs affecting Mozilla Firefox and Thunderbird products, specifically in versions Firefox ESR 115.34.0, Firefox ESR 140.9.0, Thunderbird ESR 140.9.0, Firefox 149.0.1, and Thunderbird 149.0.1. These vulnerabilities involve memory corruption issues that could potentially allow an attacker to execute arbitrary code. Mozilla has addressed these issues by releasing patched versions Firefox 149.0.2, Firefox ESR 115.34.1, Firefox ESR 140.9.1, Thunderbird 149.0.2, and Thunderbird 140.9.1. The vulnerabilities are categorized under CWE-119 (Improper Restriction of Operations within the Bounds of a Memory Buffer) and CWE-787 (Out-of-bounds Write). The CVSS v3.1 base score is 9.8, indicating critical severity with network attack vector, low attack complexity, no privileges required, no user interaction, and high impact on confidentiality, integrity, and availability.
Potential Impact
The vulnerabilities could lead to arbitrary code execution due to memory corruption, posing a critical risk to affected systems. Exploitation could compromise confidentiality, integrity, and availability of the affected applications. No known exploits in the wild have been reported at the time of disclosure.
Mitigation Recommendations
Mozilla has released official fixes for these vulnerabilities in Firefox 149.0.2, Firefox ESR 115.34.1, Firefox ESR 140.9.1, Thunderbird 149.0.2, and Thunderbird 140.9.1. Users and administrators should update to these fixed versions immediately to mitigate the risk. Patch status is confirmed by the vendor advisories linked in the report.
Technical Details
- Data Version
- 5.2
- Assigner Short Name
- mozilla
- Date Reserved
- 2026-04-07T12:43:11.413Z
- Cvss Version
- null
- State
- PUBLISHED
- Remediation Level
- null
- Vendor Advisory Urls
- [{"url":"https://www.mozilla.org/security/advisories/mfsa2026-25/","vendor":"Mozilla"},{"url":"https://www.mozilla.org/security/advisories/mfsa2026-26/","vendor":"Mozilla"},{"url":"https://www.mozilla.org/security/advisories/mfsa2026-27/","vendor":"Mozilla"}]
Threat ID: 69d50016aaed68159a219cd3
Added to database: 04/07/2026, 13:01:10 UTC
Last enriched: 07/15/2026, 09:34:16 UTC
Last updated: 07/31/2026, 19:22:59 UTC
Views: 224
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