CVE-2026-109739

Deferred Deferred - Pending Action

Privilege Escalation in Firefox WebExtensions

Publication date: 2026-10-13

Last updated on: 2026-10-14

Assigner: Mozilla Corporation

Description

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

CVSS Scores

EPSS Scores

Probability:
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Meta Information

Published

2026-10-13

Last Modified

2026-10-14

Generated

2026-10-19

AI Q&A

2026-10-13

EPSS Evaluated

2026-10-18

NVD

CVE-2026-109739

EUVD

EUVD-2026-98501

Affected Vendors & Products

Vendor	Product	Version / Range
mozilla	firefox	158

Helpful Resources

Exploitability

CWE

KEV

CWE ID	Description
CWE-269	The product does not properly assign, modify, track, or check privileges for an actor, creating an unintended sphere of control for that actor.

Attack-Flow Graph

Executive Summary

This is a privilege escalation vulnerability in the WebExtensions component of Firefox. It allows an attacker with limited access to gain higher privileges within the browser. The issue was resolved in Firefox version 158.

Detection Guidance

This vulnerability is specific to Firefox 158 and Thunderbird 158, so detection involves checking the installed versions of these applications. Use commands like 'firefox --version' or 'thunderbird --version' to verify if your system is running a vulnerable version. If the version is below 158, the system is vulnerable.

Impact Analysis

If exploited, this vulnerability could let an attacker perform actions they are not authorized to do, such as accessing sensitive data or installing malicious extensions. Users running vulnerable Firefox versions are at risk.

Mitigation Strategies

Update Firefox to version 158 or later to address the privilege escalation vulnerability in the WebExtensions component.

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