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CVE-2026-2763 Mozilla CVE debrief

CVE-2026-2763 is a critical use-after-free vulnerability in the JavaScript Engine component of Mozilla Firefox. The vulnerability was publicly disclosed on February 24, 2026, and was modified on June 30, 2026. The CVSS score for this vulnerability is 9.8, indicating a critical severity level. The vulnerability was fixed in Firefox 148, Firefox ESR 115.33, Firefox ESR 140.8, Thunderbird 148, and Thunderbird 140.8.

Vendor
Mozilla
Product
Firefox
CVSS
CRITICAL 9.8
CISA KEV
Not listed in stored evidence
Original CVE published
2026-02-24
Original CVE updated
2026-07-15
Advisory published
2026-02-24
Advisory updated
2026-07-15

Who should care

Organizations and individuals who use Mozilla Firefox, Firefox ESR, Thunderbird, or other affected products should prioritize patching this vulnerability. The critical severity level and high CVSS score indicate a significant risk of exploitation. Mozilla has provided security advisories and patches to address this vulnerability.

Technical summary

The CVE-2026-2763 vulnerability is a use-after-free issue in the JavaScript Engine component of Mozilla Firefox. This type of vulnerability occurs when a program attempts to access memory that has already been freed or deleted. An attacker could potentially exploit this vulnerability to execute arbitrary code or cause a denial-of-service condition. The vulnerability affects multiple Mozilla products, including Firefox, Firefox ESR, and Thunderbird.

Defensive priority

Patching this vulnerability is a high priority due to its critical severity level and high CVSS score. Organizations should prioritize applying the available patches to prevent potential exploitation.

Recommended defensive actions

  • Apply patches for Firefox 148, Firefox ESR 115.33, Firefox ESR 140.8, Thunderbird 148, and Thunderbird 140.8.
  • Ensure all affected Mozilla products are updated to the latest versions.
  • Monitor for any signs of exploitation or suspicious activity.
  • Consider implementing additional security measures, such as network segmentation and intrusion detection.
  • Review and update incident response plans to address potential exploitation.

Evidence notes

The CVE-2026-2763 vulnerability was publicly disclosed on February 24, 2026, and was modified on June 30, 2026. The CVSS score for this vulnerability is 9.8, indicating a critical severity level. Mozilla has provided security advisories and patches to address this vulnerability.

Sources and references

Verified primary and authoritative sources

  • CVE-2026-2763 CVE Program record

    Publisher, destination, and source semantics verified

    URL: https://www.cve.org/CVERecord?id=CVE-2026-2763

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

  • CVE-2026-2763 NVD vulnerability detail

    Publisher, destination, and source semantics verified

    URL: https://nvd.nist.gov/vuln/detail/CVE-2026-2763

    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.