CVE-2026-4723
Published: 24 March 2026
Summary
CVE-2026-4723 is a critical-severity Use After Free (CWE-416) vulnerability in Mozilla Firefox. Its CVSS base score is 9.8 (Critical).
Operationally, exploitation aligns with the MITRE ATT&CK technique Drive-by Compromise (T1189); ranked at the 6.2th percentile by exploit likelihood (below the median); it is not currently listed in the CISA KEV catalog.
The strongest mitigations our analysis identified are NIST 800-53 SI-2 (Flaw Remediation) and SC-39 (Process Isolation).
Threat & Defense at a Glance
Threat & Defense Details
Mitigating Controls (NIST 800-53 r5)AI
Timely flaw remediation ensures application of patches like Firefox 149, directly eliminating the use-after-free vulnerability in the JavaScript engine.
Memory protection safeguards such as ASLR and DEP hinder exploitation of use-after-free memory corruption in the JavaScript engine.
Process isolation via browser sandboxing confines potential arbitrary code execution from the JavaScript engine vulnerability.
MITRE ATT&CK Enterprise TechniquesAI
Why these techniques?
UAF in browser JS engine directly enables RCE via malicious web content (drive-by) and client app exploitation without auth/UI.
NVD Description
Use-after-free in the JavaScript Engine component. This vulnerability was fixed in Firefox 149 and Thunderbird 149.
Deeper analysisAI
CVE-2026-4723 is a use-after-free vulnerability (CWE-416) in the JavaScript Engine component of Mozilla Firefox and Thunderbird. This flaw allows memory corruption after an object is freed but continues to be referenced, and it was fixed in Firefox version 149 and Thunderbird version 149.
The vulnerability carries a CVSS v3.1 base score of 9.8 (AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H), marking it as critical. Remote attackers require no privileges or user interaction to exploit it over the network with low complexity, potentially achieving high-impact effects on confidentiality, integrity, and availability, such as arbitrary code execution within the browser sandbox.
Mozilla's security advisories MFSA2026-20 and MFSA2026-23 describe the vulnerability and confirm the patches in Firefox 149 and Thunderbird 149 as the primary mitigation. Additional technical details are available in Bugzilla entry 2013573.
Details
- CWE(s)