CVE-2026-100818
Critical
Description
Sandbox escape due to use-after-free in the Widget: Gtk component. This vulnerability was fixed in Firefox ESR 153.4, Thunderbird 157, Thunderbird 140.17, Thunderbird 153.4, Firefox 157, and Firefox ESR 140.17.
SeverityCritical
CVSS9.6
Exploit probability—
Product
Mozilla Firefox
PublishedSep 29, 2026
First seenSep 29, 2026
Weakness typeCWE-416Use after free
How to fix
Update
- mozilla firefox140.17.0, 153.4.0, 157.0.0 or later
- mozilla thunderbird140.17.0, 153.4.0, 157.0 or later
Affected products
| Product | Affected versions | Fixed in |
|---|---|---|
| mozilla firefox | v < 140.17.0, 141.0 ≤ v < 153.4.0, 154.0.0 ≤ v < 157.0.0 | 140.17.0, 153.4.0, 157.0.0 |
| mozilla thunderbird | v < 140.17.0, 141.0 ≤ v < 153.4.0, 154.0 ≤ v < 157.0 | 140.17.0, 153.4.0, 157.0 |
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.