CVE-2026-84142: mozilla firefox, mozilla thunderbird

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

Internally found bugs present in Thunderbird 154. 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 and Thunderbird 155.

Affected products (NVD): mozilla firefox, mozilla thunderbird

Fixed in (NVD): 155.0.0, 155.0

Weakness: CWE-119, CWE-200

Source: NVD CVE-2026-84142

References

• https://bugzilla.mozilla.org/buglist.cgi?bug_id=2029421%2C2040889%2C2045313%2C2045435%2C2053578%2C2058621%2C2058626
• https://bugzilla.mozilla.org/buglist.cgi?bug_id=2048796%2C2053150%2C2057356
• https://www.mozilla.org/security/advisories/mfsa2026-82/
• https://www.mozilla.org/security/advisories/mfsa2026-86/

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