Vulnerability Details 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.
Exploit prediction scoring system (EPSS) score
EPSS Score 0.001
EPSS Ranking 20.2%
CVSS Severity
CVSS v3 Score 9.8
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://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/
Products affected by CVE-2026-5731
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cpe:2.3:a:mozilla:firefox:115.34.0
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cpe:2.3:a:mozilla:firefox:140.9.0
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cpe:2.3:a:mozilla:firefox:149.0.1
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cpe:2.3:a:mozilla:thunderbird:140.9.0
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cpe:2.3:a:mozilla:thunderbird:149.0.1