CVE-2026-2776 is a security vulnerability identified in the Telemetry component of Mozilla Firefox, specifically affecting versions prior to Firefox 148 and Firefox ESR versions prior to 115.33 and 140.8. The root cause is incorrect boundary condition checks within the telemetry subsystem, which leads to a sandbox escape. The sandbox is a critical security mechanism designed to isolate browser processes and limit the impact of malicious code execution. By exploiting this flaw, an attacker can break out of the sandbox environment, potentially gaining higher privileges on the host system than intended by the browser's security model. This could enable execution of arbitrary code, access to sensitive data, or further compromise of the underlying operating system. The vulnerability does not require user interaction or authentication, increasing its risk profile. Although no active exploits have been reported in the wild, the technical nature of the flaw and its impact on sandbox integrity make it a significant threat. The absence of a CVSS score suggests the vulnerability is newly disclosed, and detailed exploitability metrics are pending. The Telemetry component collects usage and performance data, and its exposure to boundary condition errors indicates insufficient input validation or memory handling, common causes of sandbox escapes. This vulnerability underscores the importance of rigorous boundary checks in security-critical components like telemetry, which often interact with external data sources or processes.

The primary impact of CVE-2026-2776 is the compromise of the sandbox security boundary in Firefox, which is designed to contain potentially malicious code within a restricted environment. Successful exploitation could allow attackers to execute arbitrary code with elevated privileges on the victim's machine, leading to full system compromise. This threatens confidentiality, integrity, and availability of affected systems. Organizations relying on Firefox for secure web browsing, especially those handling sensitive data or operating in regulated industries, face increased risk of data breaches, espionage, or disruption. The vulnerability affects all users running vulnerable Firefox versions, including enterprise environments using Firefox ESR. Since no authentication or user interaction is required, automated exploitation is feasible once an exploit is developed, increasing the threat scope. The lack of known exploits currently provides a window for mitigation, but the potential for rapid weaponization exists. This vulnerability could also be leveraged in targeted attacks against high-value targets, including government agencies, financial institutions, and critical infrastructure operators. The global user base of Firefox means the impact is widespread, with particular concern for countries and sectors where Firefox is a primary browser.

To mitigate CVE-2026-2776, organizations and users should promptly update Firefox to version 148 or later, or Firefox ESR to versions 115.33 or 140.8 and above once these patches are released. Until patches are available, disabling the Telemetry component can reduce the attack surface, as the vulnerability resides in this subsystem. This can be done via Firefox configuration settings (e.g., setting 'toolkit.telemetry.enabled' to false). Employing application whitelisting and sandboxing at the OS level can provide additional containment. Monitoring network traffic and logs for unusual telemetry-related activity may help detect exploitation attempts. Organizations should also review endpoint protection policies to detect anomalous process behavior indicative of sandbox escapes. Regularly updating all software components and applying security patches promptly is critical. Security teams should prepare incident response plans for potential exploitation scenarios involving sandbox escapes. Finally, educating users about the importance of browser updates and safe browsing practices remains essential.