CVE-2026-2767 Mozilla CVE debrief

Who should care

Organizations and individuals using Mozilla Firefox, Firefox ESR, Thunderbird, or Thunderbird ESR should prioritize patching this vulnerability. The vulnerability's critical severity and high CVSS score indicate a significant risk. Additionally, defenders should review the vendor-provided advisories for specific mitigation guidance.

Technical summary

CVE-2026-2767 is a use-after-free vulnerability in the JavaScript: WebAssembly component of Mozilla Firefox, Firefox ESR, Thunderbird, and Thunderbird ESR. The vulnerability occurs when the browser attempts to access memory after it has been freed, potentially leading to arbitrary code execution. The CVSS vector for this vulnerability is CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H, indicating a high impact on confidentiality, integrity, and availability. The vulnerability was fixed in Firefox 148, Firefox ESR 140.8, Thunderbird 148, and Thunderbird 140.8.

Defensive priority

This vulnerability has a high defensive priority due to its critical severity and high CVSS score. Defenders should prioritize patching this vulnerability to prevent potential exploitation.

Recommended defensive actions

• Apply patches: Upgrade to Firefox 148, Firefox ESR 140.8, Thunderbird 148, or Thunderbird 140.8 to address the vulnerability.
• Review vendor advisories: Refer to Mozilla's security advisories for specific mitigation guidance and additional information.
• Inventory management: Ensure that all instances of Mozilla Firefox, Firefox ESR, Thunderbird, and Thunderbird ESR are updated to the patched versions.
• Monitor for exploitation attempts: Implement monitoring to detect potential exploitation attempts and review logs for suspicious activity.
• Implement compensating controls: Consider implementing compensating controls, such as network segmentation or access restrictions, to reduce the attack surface.

Evidence notes

The CVE-2026-2767 vulnerability was identified in the JavaScript: WebAssembly component of Mozilla Firefox, Firefox ESR, Thunderbird, and Thunderbird ESR. The vulnerability has a CVSS score of 9.8 and a severity of CRITICAL. The CVE was published on 2026-02-24T14:16:25.080Z and last modified on 2026-06-30T03:18:17.227Z. Mozilla has provided advisories for this vulnerability, which can be found on their security advisories page.

Sources and 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.