CVE-2026-84142

Internally found bugs fixed in Thunderbird 155

Published Sep 1, 2026 CVSS 3.1 · 9.8 Critical EPSS < 1% KEV · Not listed
Description
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.

Remediation

No solution or workaround provided in the CVE record

Tracking

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Advisories

No advisories available
History
Type Values Removed Values Added
Weaknesses CWE-416
CWE-787
Type Values Removed Values Added
Weaknesses CWE-200
Metrics ssvc

{'options': {'Automatable': 'yes', 'Exploitation': 'none', 'Technical Impact': 'total'}, 'version': '2.0.3'}

Type Values Removed Values Added
First Time appeared Mozilla thunderbird
Weaknesses CWE-119
CPEs cpe:2.3:a:mozilla:firefox:*:*:*:*:*:*:*:*
cpe:2.3:a:mozilla:thunderbird:*:*:*:*:*:*:*:*
Vendors & Products Mozilla thunderbird
Metrics cvssV3_1

{'score': 9.8, 'vector': 'CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H'}

Type Values Removed Values Added
Weaknesses CWE-416
CWE-787
Type Values Removed Values Added
Weaknesses CWE-787
Type Values Removed Values Added
Description Internally found bugs present in Firefox 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. 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.
Title Internally found bugs fixed in Firefox 155 Internally found bugs fixed in Thunderbird 155
References
Type Values Removed Values Added
Weaknesses CWE-787
Type Values Removed Values Added
First Time appeared Mozilla
Mozilla firefox
Vendors & Products Mozilla
Mozilla firefox
Type Values Removed Values Added
Description Internally found bugs present in Firefox 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.
Title Internally found bugs fixed in Firefox 155
References
Weaknesses

Sources

Status
PUBLISHED
Assigner
mozilla
Published
Updated
Sep 3, 2026, 5:23 PM
Reserved
Sep 1, 2026, 7:26 AM
Status
Modified
Published
Sep 1, 2026, 1:20 PM
Modified
Sep 3, 2026, 6:17 PM