CVE-2026-4701
Published: 24 March 2026
Description
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.
Mitigating Controls (NIST 800-53 r5)AI
Directly requires timely patching of the use-after-free vulnerability in the JavaScript engine to the fixed Firefox and Thunderbird versions, preventing exploitation.
Implements memory protections such as ASLR and DEP that raise the bar for successful exploitation of the use-after-free in the JavaScript engine.
Enables vulnerability scanning to identify systems running affected versions of Firefox, Firefox ESR, or Thunderbird prior to the fixed releases.
Security SummaryAI
CVE-2026-4701 is a use-after-free vulnerability (CWE-416) in the JavaScript Engine component of Mozilla products. It affects Firefox, Firefox ESR, and Thunderbird versions prior to the fixed releases of Firefox 149, Firefox ESR 140.9, Thunderbird 149, and Thunderbird 140.9. The vulnerability was publicly disclosed on 2026-03-24.
The vulnerability carries a CVSS v3.1 base score of 9.8 (AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H), indicating it is exploitable remotely over the network by unauthenticated attackers with low attack complexity and no user interaction. Successful exploitation can result in high impacts to confidentiality, integrity, and availability, potentially enabling arbitrary code execution within the context of the affected browser or mail client.
Mozilla security advisories (MFSA2026-20, MFSA2026-22, MFSA2026-23, and MFSA2026-24) and Bugzilla entry 2009303 detail the issue and confirm mitigation through updates to the specified fixed versions. Security practitioners should prioritize patching affected installations to Firefox 149, Firefox ESR 140.9, Thunderbird 149, or Thunderbird 140.9.
Details
- CWE(s)
Affected Products
MITRE ATT&CK Enterprise TechniquesAI
Why these techniques?
Use-after-free in JS engine directly enables remote arbitrary code execution on client (browser/mail) via crafted JavaScript, mapping to client exploitation and JS interpreter abuse.