CVE-2026-2771 is a security vulnerability identified in the Mozilla Firefox web browser, specifically affecting versions earlier than 148 and Firefox ESR versions earlier than 115.33 and 140.8. The vulnerability arises from undefined behavior within the Document Object Model (DOM) Core and HTML components, which are fundamental to how Firefox processes and renders web content. Undefined behavior in these components can lead to unpredictable browser states, potentially enabling attackers to execute arbitrary code, cause memory corruption, or bypass security controls. Although no public exploits have been reported to date, the nature of the flaw suggests that an attacker could craft malicious web content to trigger this vulnerability when rendered by the browser. This could lead to compromise of user data, session hijacking, or browser crashes, impacting confidentiality, integrity, and availability. The vulnerability affects all platforms running the vulnerable Firefox versions, including Windows, macOS, and Linux. The absence of a CVSS score indicates that Mozilla has not yet provided a detailed severity rating, but the core nature of the affected components and the potential for exploitation warrant a high level of concern. The vulnerability was reserved and published in February 2026, indicating recent discovery and disclosure. No patches or exploit indicators are currently available, emphasizing the need for vigilance and prompt updates once fixes are released.

If exploited, this vulnerability could allow attackers to execute arbitrary code within the context of the browser, potentially leading to unauthorized access to sensitive information such as cookies, stored credentials, or browsing history. It could also enable attackers to manipulate web content or perform actions on behalf of the user, undermining the integrity of web sessions. Additionally, exploitation might cause browser crashes or denial of service, affecting availability. Organizations relying on Firefox for secure web access, including government agencies, financial institutions, and enterprises, could face data breaches, loss of user trust, and operational disruptions. The broad user base of Firefox worldwide increases the potential impact scope. Since the vulnerability involves core browser components, the risk extends to any web-based application accessed via the affected browsers. The lack of known exploits currently reduces immediate risk but does not eliminate the threat, as attackers may develop exploits once patches are released or details become public.

Organizations and users should monitor Mozilla’s official channels for the release of security patches addressing CVE-2026-2771 and apply updates promptly to affected Firefox versions. Until patches are available, consider implementing browser hardening techniques such as disabling JavaScript or restricting access to untrusted websites through network-level controls or browser extensions that limit script execution. Employ endpoint protection solutions capable of detecting anomalous browser behavior indicative of exploitation attempts. Educate users about the risks of visiting untrusted websites and clicking on suspicious links. For enterprise environments, consider deploying browser isolation technologies to contain potential exploitation. Regularly audit and update browser configurations to minimize attack surface, including disabling unnecessary plugins or extensions. Maintain up-to-date backups and incident response plans to mitigate potential damage from exploitation. Finally, monitor threat intelligence feeds for any emerging exploit activity related to this vulnerability.