Cyber Resilience

CVE-2026-4724

Mozilla Firefox ≤ 149.0

Published
24 March 2026
Modified
13 April 2026
Patch / advisory
View advisory
CVSS Score v3.1 9.1
Click a component to see what it means
Raw vectorCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N
EPSS Score 0.0032 25th percentile
Risk Priority 67 floored blend · peak EPSS

Summary

CVE-2026-4724 is a critical-severity Reliance on Undefined, Unspecified, or Implementation-Defined Behavior (CWE-758) vulnerability in Mozilla Firefox. Its CVSS base score is 9.1 (Critical).

Operationally, exploitation aligns with the MITRE ATT&CK technique Exploitation for Privilege Escalation (T1068); ranked at the 25th percentile by exploit likelihood (below the median); it is not currently listed in the CISA KEV catalog.

The strongest mitigations our analysis identified map to SA-11 (Developer Testing and Evaluation) and SA-15 (Development Process, Standards, and Tools) — see the control section below for these in your framework.

Deeper analysis AI-assisted summary

Synthesised by an AI model from the NVD description and linked references — a reading aid, not an authoritative source.

CVE-2026-4724 is a vulnerability involving undefined behavior in the Audio/Video component of Mozilla Firefox and Thunderbird. It affects versions of these browsers prior to 149 and is classified under CWE-758 (Reliance on Undefined, Unspecified, or Implementation-Defined Behavior). The issue carries a CVSS v3.1 base score of 9.1, indicating critical severity due to its potential for high impact on confidentiality and integrity.

Remote attackers can exploit this vulnerability over a network with low complexity, requiring no privileges or user interaction. Successful exploitation allows attackers to achieve high confidentiality impact by accessing sensitive data and high integrity impact by modifying application data, without affecting availability or changing the scope.

Mozilla's security advisories (MFSA 2026-20 and MFSA 2026-23) and the associated Bugzilla entry detail the fix implemented in Firefox 149 and Thunderbird 149. Security practitioners should prioritize updating affected browsers to these versions for mitigation.

EU & UK References

Vulnerability Data

Undefined behavior in the Audio/Video component. This vulnerability was fixed in Firefox 149 and Thunderbird 149.

CWE(s)
CWE-758

Related Threats

MITRE ATT&CK Enterprise Techniques

T1068 Exploitation for Privilege Escalation Privilege Escalation
Adversaries may exploit software vulnerabilities in an attempt to elevate privileges.
attack.mitre.org →
T1190 Exploit Public-Facing Application Initial Access
Adversaries may attempt to exploit a weakness in an Internet-facing host or system to initially access a network.
attack.mitre.org →
T1203 Exploitation for Client Execution Execution
Adversaries may exploit software vulnerabilities in client applications to execute code.
attack.mitre.org →
T1210 Exploitation of Remote Services Lateral Movement
Adversaries may exploit remote services to gain unauthorized access to internal systems once inside of a network.
attack.mitre.org →
T1212 Exploitation for Credential Access Credential Access
Adversaries may exploit software vulnerabilities in an attempt to collect credentials.
attack.mitre.org →
T1687 Exploitation for Defense Impairment Defense Impairment
Adversaries may exploit vulnerabilities in security software, infrastructure, or defensive components to degrade, disable, or otherwise continue to impair their ability to prevent, detect, or respond to malicious activity.
attack.mitre.org →
Derived from this CVE’s CWE(s) via the direct CWE→ATT&CK cross-walk.

CVEs Like This One

CVE-2026-4718Same product: Mozilla Firefox
CVE-2024-4774Same product: Mozilla Firefox
CVE-2024-5700Same product: Mozilla Firefox
CVE-2026-4705Same product: Mozilla Firefox
CVE-2025-1016Same product: Mozilla Firefox
CVE-2024-6615Same product: Mozilla Firefox
CVE-2024-10467Same product: Mozilla Firefox
CVE-2026-2785Same product: Mozilla Firefox
CVE-2026-2792Same product: Mozilla Firefox
CVE-2025-1020Same product: Mozilla Firefox

Affected Assets

mozilla
firefox
≤ 149.0
mozilla
thunderbird
≤ 149.0

Mitigating Controls

Mitigating Controls (NIST 800-53 r5) AI

SA-11 Developer Testing and Evaluation good match

Developer testing and evaluation can discover reliance on undefined behavior through cross-platform or stress testing.

SA-15 Development Process, Standards, and Tools partial match

Mandating a documented development process and coding standards directly discourages dependence on unspecified behavior.

SA-8 Security and Privacy Engineering Principles partial match

Engineering principles can require use of only well-defined language and API behaviors during development.

Mitigating Controls (NIST CSF 2.0) AI

Derived directly from the weakness types (CWEs) cited in the NVD entry via our AI-authored CWE→CSF cross-walk (authority under review) — links open the control.

PR.PS-06 mostly match
prevents

Secure SDLC practices directly prohibit use of undefined or implementation-defined behavior in code.

PR.PS-01 partial match
prevents

Consistent hardened configurations reduce the chance of relying on unspecified implementation details.

Mitigating Controls (ISO/IEC 27001:2022 Annex A) AI

Derived directly from the weakness types (CWEs) cited in the NVD entry via our AI-authored CWE→ISO cross-walk (authority under review) — links open the control.

A.8.29 Security testing in development and acceptance mostly match
finds

Security testing can detect some instances of undefined behavior but does not prevent the root weakness.

A.8.25 Secure development life cycle partial match
prevents

Secure development life cycle requires defined, portable coding practices that reduce reliance on undefined behavior.

A.8.27 Secure system architecture and engineering principles partial match
degrades

Secure system architecture and engineering principles mandate use of well-specified interfaces and avoid undefined constructs.

A.8.28 Secure coding partial match
prevents

Secure coding explicitly prohibits constructs whose behavior is undefined, unspecified or implementation-defined.

References