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CVE-2026-4686 Mozilla CVE debrief

CVE-2026-4686 is a HIGH-severity vulnerability in the Graphics: Canvas2D component of Mozilla Firefox, with a CVSS score of 7.5. The vulnerability is caused by incorrect boundary conditions. This issue was addressed in Firefox 149, Firefox ESR 115.34, Firefox ESR 140.9, Thunderbird 149, and Thunderbird 140.9. Users should update to the latest versions to mitigate the risk. The CVE was published on March 24, 2026, and modified on June 30, 2026.

Vendor
Mozilla
Product
Firefox
CVSS
HIGH 7.5
CISA KEV
Not listed in stored evidence
Original CVE published
2026-03-24
Original CVE updated
2026-07-15
Advisory published
2026-03-24
Advisory updated
2026-07-15

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.

Sources and references

Verified primary and authoritative sources

  • CVE-2026-4686 CVE Program record

    Publisher, destination, and source semantics verified

    URL: https://www.cve.org/CVERecord?id=CVE-2026-4686

    CVE Program - Official CVE Program record with source-provided CVE metadata.

  • CVE-2026-4686 NVD vulnerability detail

    Publisher, destination, and source semantics verified

    URL: https://nvd.nist.gov/vuln/detail/CVE-2026-4686

    NIST National Vulnerability Database - Official NIST NVD detail page and source-specific vulnerability assessment.

Supplemental references

Methodology and review provenance

AI-assisted synthesis based on stored public vulnerability evidence. System validation, approval state, and publication status do not by themselves establish human review of this revision. PatchSiren helps prioritize defensive review and does not prove exposure or remediation on any system.