CVE-2026-2763
Published: 24 February 2026
Summary
CVE-2026-2763 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 Exploitation for Client Execution (T1203); 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 RA-5 (Vulnerability Monitoring and Scanning) and SI-16 (Memory Protection).
Deeper analysis
CVE-2026-2763 is a use-after-free vulnerability (CWE-416) in the JavaScript Engine component of Mozilla Firefox and Thunderbird products. It affects versions prior to the fixed releases, including Firefox 148, Firefox ESR 115.33, Firefox ESR 140.8, Thunderbird 148, and Thunderbird 140.8. The vulnerability was publicly disclosed on 2026-02-24 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.
An unauthenticated attacker can exploit this vulnerability remotely over the network with low complexity and no user interaction required. Successful exploitation could allow arbitrary code execution, data corruption, or denial of service within the affected browser or email client context, potentially compromising the victim's system if chained with other flaws.
Mozilla's security advisories (MFSA 2026-13 through 2026-16) and the associated Bugzilla entry detail the patch deployments in the specified versions, recommending immediate upgrades to mitigate the issue. No workarounds are mentioned in the provided references.
EU & UK References
- 🇪🇺 ENISA EUVD: EUVD-2026-8485
Vulnerability details
Use-after-free in the JavaScript Engine component. This vulnerability was fixed in Firefox 148, Firefox ESR 115.33, 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 in JS engine enables remote arbitrary code execution in client software (browser/email) with no user interaction required, directly mapping to T1203 Exploitation for Client Execution.
CVEs Like This One
Affected Assets
Mitigating Controls
Mitigating Controls (NIST 800-53 r5) AI
Requires identification, reporting, and timely correction of system flaws, directly addressing the need to patch this use-after-free vulnerability in the JavaScript engine.
Implements memory protection controls specifically designed to minimize the impact of use-after-free vulnerabilities like CVE-2026-2763.
Conducts vulnerability scanning to identify and remediate flaws such as this critical JavaScript engine vulnerability in deployed Firefox and Thunderbird instances.
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