CVE-2026-4721
Critical · CVSS 9.8Mozilla Firefox / Thunderbird — Memory safety bugs / buffer overflow / dangling pointer arbitrary code execution (CWE-120, CWE-825)
- CVSS
- 9.8
- nvd
- EPSS
- —
- KEV
- No
- Class
- other
- CWE-120, CWE-825
Description
Memory safety bugs present in Firefox ESR 115.33, Firefox ESR 140.8, Thunderbird ESR 140.8, Firefox 148 and Thunderbird 148. 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, Firefox ESR 115.34, Firefox ESR 140.9, Thunderbird 149, and Thunderbird 140.9.
Search profile — drives PoC discovery
Symbols bug_id=2013762bug_id=2015291bug_id=2016591bug_id=2016661bug_id=2016664bug_id=2017303bug_id=2017894bug_id=2018090bug_id=2018196bug_id=2018379bug_id=2019112bug_id=2022090bug_id=2022243bug_id=2022351bug_id=2022478bug_id=2022676mfsa2026-20mfsa2026-21mfsa2026-22mfsa2026-23
Keywords CVE-2026-4721Firefox memory safetyThunderbird memory corruptionFirefox 148 RCEFirefox ESR 115.33Firefox ESR 140.8Thunderbird ESR 140.8mfsa2026-20mfsa2026-21mfsa2026-22mfsa2026-23CWE-120 FirefoxCWE-825 Firefoxbuffer overflow Firefox 148dangling pointer Firefox
Versions: Firefox < 149, Firefox ESR < 115.34, Firefox ESR < 140.9, Thunderbird < 149, Thunderbird ESR < 140.9
References
- https://bugzilla.mozilla.org/buglist.cgi?bug_id=2013762%2C2015291%2C2016591%2C2016661%2C2016664%2C2017303%2C2017894%2C2018090%2C2018196%2C2018379%2C2019112%2C2022090%2C2022243%2C2022351%2C2022478%2C2022676
- https://www.mozilla.org/security/advisories/mfsa2026-20/
- https://www.mozilla.org/security/advisories/mfsa2026-21/
- https://www.mozilla.org/security/advisories/mfsa2026-22/
- https://www.mozilla.org/security/advisories/mfsa2026-23/
- https://www.mozilla.org/security/advisories/mfsa2026-24/
- https://access.redhat.com/errata/RHSA-2026:5930
- https://access.redhat.com/errata/RHSA-2026:5931
- https://access.redhat.com/errata/RHSA-2026:5932
- https://access.redhat.com/errata/RHSA-2026:6188
- https://access.redhat.com/errata/RHSA-2026:6342
- https://access.redhat.com/errata/RHSA-2026:6917
Status: enriched · ingested 2026-06-30T06:00:22.000Z · profiled 2026-07-01T18:30:14.000Z