Privilege Escalation Vulnerability in Firefox WebExtensions Component
CVE-2026-109739

8.8HIGH

Key Information:

Vendor

Mozilla
Status
Firefox
Thunderbird
Vendor
CVE Published:
13 October 2026

What is CVE-2026-109739?

A vulnerability has been identified in the WebExtensions component of Firefox that allows for privilege escalation. This issue arises from improper validation within the component, potentially enabling an attacker to gain elevated permissions. Users are advised to update to Firefox version 158 or later to mitigate the risks associated with this vulnerability.

Affected Version(s)

Firefox 158

Thunderbird 158

References

https://bugzilla.mozilla.org/show_bug.cgi?id=2049069
https://www.mozilla.org/security/advisories/mfsa2026-106/
https://www.mozilla.org/security/advisories/mfsa2026-109/

CVSS V3.1

Score:
8.8
Severity:
HIGH
Confidentiality:
High
Integrity:
High
Availability:
High
Attack Vector:
Network
Attack Complexity:
Low
Privileges Required:
Low
User Interaction:
None
Scope:
Unchanged

Timeline

  • Vulnerability published

  • Vulnerability Reserved

Credit

Tomoya Nakanishi
.