CVE-2026-2766 is a use-after-free vulnerability affecting the Just-In-Time (JIT) compilation component of the JavaScript Engine in Mozilla Firefox. This type of vulnerability (CWE-416) occurs when the program continues to use memory after it has been freed, potentially leading to arbitrary code execution or other serious impacts. The vulnerability has a CVSS v3.1 base score of 9.8, indicating critical severity with network attack vector, no required privileges or user interaction, and full impact on confidentiality, integrity, and availability. Mozilla fixed this vulnerability in Firefox 148 and Firefox ESR 140.8, as documented in their security advisories MFSA 2026-13 and MFSA 2026-15.

Successful exploitation of CVE-2026-2766 could allow an attacker to execute arbitrary code remotely without any user interaction or privileges, leading to full compromise of the affected Firefox browser environment. This includes potential loss of confidentiality, integrity, and availability of user data and system resources accessible through the browser. The vulnerability is critical due to its high CVSS score and the nature of use-after-free bugs in memory management.

Mozilla has released official fixes for this vulnerability in Firefox 148 and Firefox ESR 140.8. Users and administrators should update to these versions or later to remediate the issue. Since this is not a cloud service, remediation depends on applying the vendor's official patches. There are no indications that the vulnerability is already mitigated or requires no action. Patch status is confirmed by Mozilla advisories MFSA 2026-13 and MFSA 2026-15.