CVE-2026-109739
High
Description
Privilege escalation in the WebExtensions component. This vulnerability was fixed in Firefox 158 and Thunderbird 158.
SeverityHigh
CVSS8.8
Exploit probability—
ProductFirefox
PublishedOct 13, 2026
First seenOct 13, 2026
Weakness typeCWE-269Improper privilege management
How to fix
Update
- Firefox158 or later
- Thunderbird158 or later
Affected products
| Product | Affected versions | Fixed in |
|---|---|---|
| Firefox | No range specified | 158 |
| Thunderbird | No range specified | 158 |
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.