CVE-2025-2857 is a critical security vulnerability identified in Mozilla Firefox's inter-process communication (IPC) code on Windows platforms. The flaw arises from incorrect handle management, where a compromised child process can manipulate the parent process into returning an overly powerful handle. This handle can be leveraged to escape the browser's sandbox, a security mechanism designed to isolate processes and limit the impact of exploits. The vulnerability is similar to a recent Chrome sandbox escape (CVE-2025-2783), indicating a pattern in modern browser IPC implementations. A sandbox escape allows an attacker to break out of the restricted environment, potentially gaining elevated privileges on the host system. The vulnerability affects Firefox versions earlier than 136.0.4 and ESR versions earlier than 128.8.1 and 115.21.1, exclusively on Windows; other operating systems are unaffected. The CVSS v3.1 score is 10.0, reflecting critical severity with network attack vector, low attack complexity, no privileges or user interaction required, and impacts on confidentiality, integrity, and availability. While no known exploits are publicly reported, the presence of similar exploits in the wild for Chrome underscores the urgency of addressing this issue. The vulnerability is classified under CWE-668, which relates to improper handle or resource management leading to security issues. No official patches were linked at the time of reporting, but updates to Firefox versions 136.0.4 and ESR 128.8.1/115.21.1 are expected to remediate the flaw.

The impact of CVE-2025-2857 on European organizations is significant due to the critical nature of the vulnerability and the widespread use of Firefox on Windows systems. Successful exploitation allows attackers to escape the browser sandbox, potentially leading to full system compromise, including unauthorized access to sensitive data, installation of persistent malware, and disruption of system operations. This threatens confidentiality, integrity, and availability of organizational assets. European entities in sectors such as finance, government, healthcare, and critical infrastructure, which rely heavily on secure browsing environments, are particularly at risk. The vulnerability's ease of exploitation—requiring no privileges or user interaction—means attackers can remotely compromise systems via malicious web content or compromised websites. This elevates the risk of widespread attacks, including targeted espionage or ransomware campaigns. The lack of known public exploits currently provides a limited window for mitigation before potential weaponization. Organizations failing to update Firefox promptly may face increased exposure to advanced persistent threats and cybercriminal activities.

To mitigate CVE-2025-2857, European organizations should immediately update all affected Firefox installations on Windows to version 136.0.4 or later, or ESR versions 128.8.1/115.21.1 or later once available. Until patches are applied, organizations should consider deploying application control policies to restrict execution of untrusted code and limit browser capabilities. Employing sandbox hardening techniques, such as enabling Windows Defender Application Guard or similar isolation technologies, can reduce the risk of sandbox escapes. Network-level protections, including web filtering and intrusion prevention systems, should be configured to block access to known malicious sites and suspicious content. Security teams should monitor for unusual process behaviors indicative of sandbox escape attempts. Additionally, educating users about the risks of visiting untrusted websites and maintaining up-to-date endpoint detection and response (EDR) solutions will enhance detection and response capabilities. Coordinating with Mozilla security advisories for timely patch releases and guidance is essential. Finally, organizations should review and tighten IPC-related configurations and permissions where feasible to minimize attack surface.