CVE-2026-109739: Privilege escalation in the WebExtensions component

Published Oct 13, 2026
·
Updated

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

Affected Software

2 affected componentsFixes available
Mozilla Firefox<158
158
Mozilla Thunderbird<158
158

Remediation

Recommended actions to resolve this vulnerability, in priority order.

  1. Upgrade

    Upgrade to a fixed release to a version that resolves this vulnerability.

    Fixed in 158
  2. Upgrade

    Upgrade Firefox to a version that resolves this vulnerability.

    Fixed in 158
  3. Upgrade

    Upgrade Thunderbird to a version that resolves this vulnerability.

    Fixed in 158

Event History

Oct 13, 2026
CVE Published
via Mozilla·12:00 AM
Data Sourced
via Mozilla·12:00 AM
DescriptionSeverityAffected Software
CVE Published
via MITRE·12:29 PM
Data Sourced
via MITRE·12:29 PM
Description
Data Sourced
via NVD·01:17 PM
Description

Parent advisories

This vulnerability appears in the following advisories.

Peer vulnerabilities

Found alongside the following vulnerabilities.

Frequently Asked Questions

1

Which Firefox versions are affected?

The issue was fixed in Firefox 158. The provided data does not identify the first affected version or whether any earlier release branches are affected.

2

What access would an attacker need to exploit this issue?

The provided data identifies the WebExtensions component and describes a privilege escalation, but it does not specify the attacker’s required access, extension permissions, or user interaction requirements.

3

How can I determine whether remediation has been applied?

Verify that Firefox has been updated to version 158 or later. The provided data does not include indicators of compromise or other detection guidance.

Company

Resources

Contact

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