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
CVSS Score
9.8
EPSS Score
0.0%
EPSS Percentile
0th
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.
| Vendor | mozilla |
| Product | firefox |
| Ecosystems | |
| Industries | Technology |
| Published | Apr 7, 2026 |
| Last Updated | Apr 13, 2026 |
Stay Ahead of the Next One
Get instant alerts for mozilla firefox
Be the first to know when new critical vulnerabilities affecting mozilla firefox are published — delivered to Slack, Telegram or Discord.
Get Free Alerts →
Free · No credit card · 60 sec setup
Affected Versions
Mozilla / Firefox
All versions affected Mozilla / Thunderbird
All versions affected References
bugzilla.mozilla.org: 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 mozilla.org: https://www.mozilla.org/security/advisories/mfsa2026-25/ mozilla.org: https://www.mozilla.org/security/advisories/mfsa2026-26/ mozilla.org: https://www.mozilla.org/security/advisories/mfsa2026-27/ mozilla.org: https://www.mozilla.org/security/advisories/mfsa2026-28/ mozilla.org: https://www.mozilla.org/security/advisories/mfsa2026-29/
Credits
Brian Grinstead, Christian Holler, Tom Schuster and the Mozilla Fuzzing Team