CVE-2026-2766
Published: 24 February 2026
Summary
CVE-2026-2766 is a critical-severity Use After Free (CWE-416) vulnerability in Mozilla Firefox. Its CVSS base score is 9.8 (Critical).
Operationally, exploitation aligns with the MITRE ATT&CK technique Drive-by Compromise (T1189); ranked at the 37.3th percentile by exploit likelihood (below the median); it is not currently listed in the CISA KEV catalog.
The strongest mitigations our analysis identified are NIST 800-53 SI-16 (Memory Protection) and SI-2 (Flaw Remediation).
Deeper analysis
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.
EU & UK References
- 🇪🇺 ENISA EUVD: EUVD-2026-8489
Vulnerability details
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.
- CWE(s)
Related Threats
MITRE ATT&CK Enterprise TechniquesAI
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.
CVEs Like This One
Affected Assets
Mitigating Controls
Mitigating Controls (NIST 800-53 r5) AI
Requires timely identification, reporting, and patching of flaws like this use-after-free vulnerability in the JavaScript JIT component to prevent exploitation.
Directly implements memory protections against unauthorized code execution due to use-after-free vulnerabilities as specified in the control.
Isolates browser processes to contain potential arbitrary code execution from exploitation of the JIT use-after-free flaw.
Hardening callouts derived
Configuration rules from DISA STIG baselines that reduce the attack surface for weaknesses of the type cited by this CVE. Derived transitively via CVE→CWE→STIG over `controls_xwalks` (authoritative rows only).
Oracle Linux 8 (1 rule)
- V-248592 OL 8 must clear memory when it is freed to prevent use-after-free attacks. via CWE-416
RHEL 8 (1 rule)
- V-230279 RHEL 8 must clear memory when it is freed to prevent use-after-free attacks. via CWE-416
RHEL 9 (1 rule)
- V-257794 RHEL 9 must clear memory when it is freed to prevent use-after-free attacks. via CWE-416