CVE-2026-84143: mozilla firefox, mozilla thunderbird

CVSS 9.8 (critical) · published 2026-09-01

Internally found bugs present in Thunderbird 154, Thunderbird ESR 153.1 and Thunderbird ESR 140.14. Some of these bugs showed evidence of memory corruption or another security-relevant defect and we presume that with enough effort some of these could have been exploited. This vulnerability was fixed in Firefox 155, Firefox ESR 140.15, Firefox ESR 153.2, Thunderbird 155, Thunderbird 140.15, and Thunderbird 153.2.

Affected products (NVD): mozilla firefox, mozilla thunderbird

Fixed in (NVD): 140.15.0, 153.2.0, 155.0.0, 155.0

Weakness: CWE-119, CWE-200

Source: NVD CVE-2026-84143

References

• https://bugzilla.mozilla.org/buglist.cgi?bug_id=2048793%2C2054645%2C2057114%2C2059109%2C2061287
• https://bugzilla.mozilla.org/buglist.cgi?bug_id=2054631%2C2054657%2C2055007%2C2055681%2C2057107%2C2058087%2C2058088%2C2058090%2C2058095%2C2058101%2C2059183%2C2059185%2C2061301%2C2061325
• https://bugzilla.mozilla.org/show_bug.cgi?id=2057108
• https://www.mozilla.org/security/advisories/mfsa2026-82/
• https://www.mozilla.org/security/advisories/mfsa2026-84/
• https://www.mozilla.org/security/advisories/mfsa2026-85/
• https://www.mozilla.org/security/advisories/mfsa2026-86/
• https://www.mozilla.org/security/advisories/mfsa2026-87/
• https://www.mozilla.org/security/advisories/mfsa2026-88/

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