CVE-2026-84143
Critical
Description
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.
SeverityCritical
CVSS9.8
Exploit probability—
Product
Mozilla Firefox
PublishedSep 1, 2026
First seenSep 1, 2026
Weakness typeCWE-200Sensitive information exposure
How to fix
Update
- mozilla firefox140.15.0, 153.2.0, 155.0.0 or later
- mozilla thunderbird140.15.0, 153.2.0, 155.0 or later
Affected products
| Product | Affected versions | Fixed in |
|---|---|---|
| mozilla firefox | v < 140.15.0, 141.0.0 ≤ v < 153.2.0, 154.0.0 ≤ v < 155.0.0 | 140.15.0, 153.2.0, 155.0.0 |
| mozilla thunderbird | v < 140.15.0, 141.0 ≤ v < 153.2.0, 154.0 ≤ v < 155.0 | 140.15.0, 153.2.0, 155.0 |
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