Cyber Posture

CVE-2026-2766

Critical

Published: 24 February 2026

Published
24 February 2026
Modified
13 April 2026
KEV Added
—
Patch
—
CVSS Score 9.8 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
EPSS Score 0.0002 6.8th percentile
Risk Priority 20 60% EPSS · 20% KEV · 20% CVSS

Description

Use-after-free in the JavaScript Engine: JIT component. This vulnerability was fixed in Firefox 148, Firefox ESR 140.8, Thunderbird 148, and Thunderbird 140.8.

Mitigating Controls (NIST 800-53 r5)AI

SI-2 Flaw Remediation good match
prevent

Requires timely identification, reporting, and patching of flaws like this use-after-free vulnerability in the JavaScript JIT component to prevent exploitation.

SI-16 Memory Protection good match
prevent

Directly implements memory protections against unauthorized code execution due to use-after-free vulnerabilities as specified in the control.

SC-39 Process Isolation partial match
prevent

Isolates browser processes to contain potential arbitrary code execution from exploitation of the JIT use-after-free flaw.

Security SummaryAI

CVE-2026-2766 is a use-after-free vulnerability (CWE-416) in the JavaScript Engine's JIT component, affecting Mozilla Firefox versions prior to 148, Firefox ESR prior to 140.8, Thunderbird prior to 148, and Thunderbird prior to 140.8. The issue was publicly disclosed on February 24, 2026, and carries a CVSS v3.1 base score of 9.8, indicating critical severity due to its potential for high impact on confidentiality, integrity, and availability.

The vulnerability can be exploited remotely by unauthenticated attackers over the network with low complexity and no user interaction required (AV:N/AC:L/PR:N/UI:N/S:U). Successful exploitation could allow attackers to achieve high-impact effects, including arbitrary code execution, data corruption, or denial of service within the affected browser or email client processes.

Mozilla's security advisories (MFSA 2026-13, 15, 16, and 17) and the associated Bugzilla entry detail the patch releases that address the flaw, recommending immediate upgrades to Firefox 148, Firefox ESR 140.8, Thunderbird 148, or Thunderbird 140.8 for mitigation. No additional workarounds are specified in the provided references.

Details

CWE(s)
CWE-416

Affected Products

mozilla
firefox
≤ 140.8.0 · ≤ 148.0
mozilla
thunderbird
≤ 140.8.0 · ≤ 148.0

MITRE ATT&CK Enterprise TechniquesAI

T1189 Drive-by Compromise Initial Access
Adversaries may gain access to a system through a user visiting a website over the normal course of browsing.
attack.mitre.org →
T1203 Exploitation for Client Execution Execution
Adversaries may exploit software vulnerabilities in client applications to execute code.
attack.mitre.org →
Why these techniques?

Use-after-free RCE in browser/Thunderbird JS JIT engine directly enables drive-by compromise via malicious web content and exploitation for client execution with no user interaction required.

Confidence: HIGH · MITRE ATT&CK Enterprise v18.1

References