Privilege Escalation in Mozilla Firefox and ESR WebExtensions
CVE-2026-16396

8.8HIGH

Key Information:

Vendor

Mozilla
Status
Firefox
Thunderbird
Vendor
CVE Published:
21 July 2026

What is CVE-2026-16396?

A privilege escalation vulnerability exists in the WebExtensions architecture of Mozilla Firefox and its Extended Support Release (ESR) version. This flaw could allow attackers to gain elevated privileges within the browser environment, potentially leading to unauthorized access or control over browser functionalities. The vulnerability has been addressed in the latest versions of Firefox 153 and Firefox ESR 140.13, emphasizing the importance of keeping browser software up-to-date to safeguard against such security threats.

Affected Version(s)

Firefox 140.13

Firefox 153

Thunderbird 140.13

References

https://bugzilla.mozilla.org/show_bug.cgi?id=2047240
https://www.mozilla.org/security/advisories/mfsa2026-68/
https://www.mozilla.org/security/advisories/mfsa2026-70/

CVSS V3.1

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

Timeline

  • Vulnerability published

  • Vulnerability Reserved

Credit

Quy Pham
.