Cyber Resilience

CVE-2026-4723

Critical

Published: 24 March 2026

Published
24 March 2026
Modified
13 April 2026
KEV Added
—
Patch
—
CVSS Score v3.1 9.8 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
EPSS Score 0.0039 31.2th percentile
Risk Priority 70 floored blend · peak EPSS

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 31.2th 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).

Deeper analysis

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.

EU & UK References

Vulnerability details

Use-after-free in the JavaScript Engine component. This vulnerability was fixed in Firefox 149 and Thunderbird 149.

CWE(s)
CWE-416

Related Threats

MITRE ATT&CK Enterprise TechniquesAI

T1189 Drive-by Compromise Initial Access
Adversaries may gain access to a system through a user visiting a website over the normal course of browsing.
attack.mitre.org →
T1203 Exploitation for Client Execution Execution
Adversaries may exploit software vulnerabilities in client applications to execute code.
attack.mitre.org →
Why these techniques?

UAF in browser JS engine directly enables RCE via malicious web content (drive-by) and client app exploitation without auth/UI.

Confidence: HIGH · MITRE ATT&CK Enterprise v19.0

CVEs Like This One

CVE-2026-24869Same product: Mozilla Firefox
CVE-2026-4711Same product: Mozilla Firefox
CVE-2026-4725Same product: Mozilla Firefox
CVE-2026-4696Same product: Mozilla Firefox
CVE-2026-3847Same product: Mozilla Firefox
CVE-2026-4691Same product: Mozilla Firefox
CVE-2026-8390Same product: Mozilla Firefox
CVE-2026-4701Same product: Mozilla Firefox
CVE-2026-2795Same product: Mozilla Firefox
CVE-2024-5694Same product: Mozilla Firefox

Affected Assets

mozilla
firefox
≤ 149.0

Mitigating Controls

Mitigating Controls (NIST 800-53 r5) AI

SI-2 Flaw Remediation good match
prevent

Timely flaw remediation ensures application of patches like Firefox 149, directly eliminating the use-after-free vulnerability in the JavaScript engine.

SI-16 Memory Protection partial match
prevent

Memory protection safeguards such as ASLR and DEP hinder exploitation of use-after-free memory corruption in the JavaScript engine.

SC-39 Process Isolation partial match
prevent

Process isolation via browser sandboxing confines potential arbitrary code execution from the JavaScript engine vulnerability.

Hardening callouts derived

Configuration rules from DISA STIG baselines that reduce the attack surface for weaknesses of the type cited by this CVE. Derived transitively via CVE→CWE→STIG over `controls_xwalks` (authoritative rows only).

Oracle Linux 8 (1 rule)
  • V-248592 OL 8 must clear memory when it is freed to prevent use-after-free attacks. via CWE-416
RHEL 8 (1 rule)
  • V-230279 RHEL 8 must clear memory when it is freed to prevent use-after-free attacks. via CWE-416
RHEL 9 (1 rule)
  • V-257794 RHEL 9 must clear memory when it is freed to prevent use-after-free attacks. via CWE-416

References