CVE-2026-4697
Published: 24 March 2026
Summary
CVE-2026-4697 is a high-severity Improper Check for Unusual or Exceptional Conditions (CWE-754) vulnerability in Mozilla Firefox. Its CVSS base score is 7.5 (High).
Operationally, exploitation aligns with the MITRE ATT&CK technique Application or System Exploitation (T1499.004); ranked at the 6.0th 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 RA-5 (Vulnerability Monitoring and Scanning).
Threat & Defense at a Glance
Threat & Defense Details
Mitigating Controls (NIST 800-53 r5)AI
Directly requires timely identification, testing, and application of patches to remediate the specific boundary condition flaw in the Web Codecs component of Firefox and Thunderbird.
Mandates vulnerability scanning to identify systems running vulnerable versions of Mozilla products affected by CVE-2026-4697.
Implements controls to limit or detect the effects of denial-of-service attacks exploiting this vulnerability to cause application crashes.
MITRE ATT&CK Enterprise TechniquesAI
Why these techniques?
The vulnerability allows remote network exploitation of a client-side boundary condition flaw in web codecs, directly causing application crashes and high availability impact with no privileges or user interaction required, mapping precisely to application/system exploitation for endpoint DoS.
NVD Description
Incorrect boundary conditions in the Audio/Video: Web Codecs component. This vulnerability was fixed in Firefox 149, Firefox ESR 140.9, Thunderbird 149, and Thunderbird 140.9.
Deeper analysisAI
CVE-2026-4697 involves incorrect boundary conditions (CWE-754) in the Audio/Video: Web Codecs component of Mozilla products. This vulnerability affects Firefox, Firefox ESR, and Thunderbird, with fixes released in Firefox 149, Firefox ESR 140.9, Thunderbird 149, and Thunderbird 140.9.
The vulnerability carries a CVSS v3.1 base score of 7.5 (AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H). Remote attackers with no privileges or user interaction can exploit it over the network with low attack complexity, achieving a high impact on availability through denial of service, such as application crashes, without compromising confidentiality or integrity.
Mozilla's security advisories MFSA 2026-20, MFSA 2026-22, MFSA 2026-23, and MFSA 2026-24, along with Bugzilla entry 2020422, provide further details on the issue and patches. Security practitioners should ensure affected systems update to the specified fixed versions for mitigation.
Details
- CWE(s)