Use-after-free Vulnerability in Firefox and Firefox ESR
CVE-2026-4711

9.8CRITICAL

Key Information:

Vendor

Mozilla
Status
Firefox
Firefox Esr
Thunderbird
Vendor
CVE Published:
24 March 2026

What is CVE-2026-4711?

A use-after-free vulnerability exists in the Widget: Cocoa component of Firefox and Firefox ESR, which could potentially lead to unexpected behavior or security breaches. This vulnerability affects users running versions of Firefox prior to 149 and Firefox ESR prior to 140.9, exposing them to risks when manipulating Cocoa widgets. It is essential for users to update their browsers to safeguard against potential exploits.

Affected Version(s)

Firefox < 149

Firefox ESR < 140.9

Thunderbird < 149

References

https://bugzilla.mozilla.org/show_bug.cgi?id=2017002
https://www.mozilla.org/security/advisories/mfsa2026-20/
https://www.mozilla.org/security/advisories/mfsa2026-22/

CVSS V3.1

Score:
9.8
Severity:
CRITICAL
Confidentiality:
High
Integrity:
High
Availability:
High
Attack Vector:
Network
Attack Complexity:
Low
Privileges Required:
None
User Interaction:
None
Scope:
Unchanged

Timeline

  • Vulnerability published

  • Vulnerability Reserved

Credit

Josh Aas
.