---
id: CVE-2026-109739
title: Privilege escalation in the WebExtensions component
summary: >-
  Privilege escalation in the WebExtensions component. This vulnerability was
  fixed in Firefox 158 and Thunderbird 158.
severity: high
cvss: 8.8
cvssVector: 'CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H'
cwe:
  - CWE-269
published: '2026-10-13'
updated: '2026-10-14'
sourceUpdated: '2026-10-14T16:17:37.327'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2026-109739'
references:
  - url: 'https://bugzilla.mozilla.org/show_bug.cgi?id=2049069'
    label: security@mozilla.org
  - url: 'https://www.mozilla.org/security/advisories/mfsa2026-106/'
    label: security@mozilla.org
  - url: 'https://www.mozilla.org/security/advisories/mfsa2026-109/'
    label: security@mozilla.org
tags:
  - nvd
  - cve.org
ingestedAt: '2026-10-13T13:27:04.003Z'
vendor: Mozilla
product: Firefox
affected:
  - Firefox
  - Thunderbird
ssvc:
  exploitation: none
  automatable: 'no'
  technicalImpact: total
  timestamp: '2026-10-14T03:59:06.635051Z'
epss: 0.00369
epssPercentile: 0.30594
---

## Overview

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

## Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.