CVE-2026-4686
Published: 24 March 2026
Summary
CVE-2026-4686 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 7.3th 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, reporting, and correction of flaws like CVE-2026-4686 through patching Firefox and Thunderbird to fixed versions, preventing remote denial-of-service crashes.
Enables vulnerability scanning to detect systems running vulnerable versions of Firefox or Thunderbird affected by CVE-2026-4686's boundary condition flaw.
Ensures receipt, dissemination, and implementation of vendor security advisories like Mozilla's MFSA for CVE-2026-4686 to facilitate prompt flaw remediation.
MITRE ATT&CK Enterprise TechniquesAI
Why these techniques?
CVE enables remote application crashes via Canvas2D boundary flaw (CWE-754), directly mapping to T1499.004 Application or System Exploitation for Endpoint DoS.
NVD Description
Incorrect boundary conditions in the Graphics: Canvas2D component. This vulnerability was fixed in Firefox 149, Firefox ESR 115.34, Firefox ESR 140.9, Thunderbird 149, and Thunderbird 140.9.
Deeper analysisAI
CVE-2026-4686 is a vulnerability involving incorrect boundary conditions in the Graphics: Canvas2D component of Mozilla Firefox and Thunderbird. It affects versions of Firefox prior to 149, Firefox ESR prior to 115.34 and 140.9, and Thunderbird prior to 149 and 140.9. The issue, classified under CWE-754 (Improper Check for Unusual or Exceptional Conditions), 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) and was publicly disclosed on March 24, 2026.
Attackers can exploit this vulnerability remotely over the network with low complexity, requiring no privileges, authentication, or user interaction. Successful exploitation results in high-impact denial of service, such as application crashes, without affecting confidentiality or integrity.
Mozilla's security advisories (MFSA 2026-20 through 2026-23) and the associated Bugzilla entry (bug 2016351) confirm the vulnerability was addressed in the listed fixed releases. Security practitioners should prioritize updating affected Firefox and Thunderbird installations to mitigate the risk of remote crashes.
Details
- CWE(s)