CVE-2026-74990
Critical
Description
Internally found bugs present in Thunderbird ESR 140.13, Thunderbird ESR 153.0 and Thunderbird 153. 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 154, Firefox ESR 115.39, Firefox ESR 140.14, Firefox ESR 153.1, Thunderbird 154, Thunderbird 140.14, and Thunderbird 153.1.
SeverityCritical
CVSS9.8
Exploit probability—
Product
Mozilla Firefox
PublishedAug 18, 2026
First seenAug 18, 2026
Weakness typeCWE-119Memory buffer bounds error
How to fix
Update
- mozilla firefox115.39.0, 140.14.0, 153.1.0 or later
- mozilla thunderbird140.14.0, 153.1.0 or later
Affected products
| Product | Affected versions | Fixed in |
|---|---|---|
| mozilla firefox | v < 115.39.0, 116.0 ≤ v < 140.14.0, 141.0 ≤ v < 153.1.0 | 115.39.0, 140.14.0, 153.1.0 |
| mozilla thunderbird | v < 140.14.0, 141.0 ≤ v < 153.1.0 | 140.14.0, 153.1.0 |
Check your version
Choose the product and enter the version you run to see whether it falls in the affected range.
In the Intelligence 360 plan
Attack Surface Management
See the assets tied to your domains, the technologies they run and known vulnerabilities in one list.