CVE-2026-109739

Firefox: Privilege escalation in the WebExtensions component

Mozilla FirefoxApplications & CMS

CVSS

8.8High

ExploitationNo known exploitationNot in CISA KEV, which does not prove it is unexploitedCISA KEV

Exploit odds (EPSS)0.37%Chance of exploitation activity in the next 30 days, higher than 29% of CVEs. Scored 23 Oct 2026FIRST EPSS

Fixed inNone listedNo source names a fixed version. Check the vendor advisory below

Published13 Oct 2026Updated 14 Oct 2026CVE List

What fixes it

No source in this snapshot names a fixed version. The vendor advisories under References are the place to check.

Privilege escalation in the WebExtensions component. This vulnerability was fixed in Firefox 158 and Thunderbird 158.

Text from CVE List