CVE-2026-4686 Mozilla CVE debrief

Who should care

This vulnerability affects users of Mozilla Firefox, Firefox ESR, and Thunderbird. System administrators and security teams should prioritize patching to prevent potential exploitation. Users of affected products should update to the latest versions to ensure their browsers are secure.

Technical summary

The vulnerability is caused by incorrect boundary conditions in the Graphics: Canvas2D component of Mozilla Firefox. This issue can be exploited remotely, and an attacker could potentially cause a denial-of-service or execute arbitrary code. The Common Vulnerability Scoring System (CVSS) score for this vulnerability is 7.5, indicating a HIGH level of severity. The CVSS vector for this vulnerability is CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H.

Defensive priority

This vulnerability has a HIGH CVSS score and is publicly known, making it a priority for patching. System administrators and security teams should prioritize patching to prevent potential exploitation.

Recommended defensive actions

• Update Firefox to version 149 or later
• Update Firefox ESR to version 115.34 or later
• Update Firefox ESR to version 140.9 or later
• Update Thunderbird to version 149 or later
• Update Thunderbird to version 140.9 or later

Evidence notes

The CVE-2026-4686 vulnerability was published on March 24, 2026, and modified on June 30, 2026. The vulnerability affects multiple Mozilla products, including Firefox, Firefox ESR, and Thunderbird. The Common Vulnerabilities and Exposures (CVE) system provides a unique identifier for this vulnerability, and the National Vulnerability Database (NVD) provides additional information and resources for mitigation.

Official resources