Mozilla Firefox — CVE-2026-4701 (Critical)

Date Mar 24, 2026

Type Vendor advisory

Signal Critical vendor advisory

Vendor / Product Mozilla · Firefox

CVE CVE-2026-4701

Critical vendor advisory CVE-2026-4701

Summary

Use-after-free in the JavaScript Engine component. This vulnerability was fixed in Firefox 149, Firefox ESR 140.9, Thunderbird 149, and Thunderbird 140.9.

Why it matters

This CVE carries a CRITICAL severity rating (CVSS 9.8) in Mozilla Firefox. Patch or mitigate promptly.

Operator check

Review CVE-2026-4701 in your asset inventory. Apply patches per vendor guidance and verify Firefox is not exposed. CVSS score: 9.8.

Sources

NVD — CVE-2026-4701 Vendor reference Vendor reference

PatchBrief uses public sources. It does not scan environments, verify exposure, or replace vendor guidance.

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