CVE-2025-4275 is a high-severity vulnerability affecting Insyde Software's InsydeH2O UEFI firmware, specifically impacting versions with Kernel 5.2 through 5.7. The vulnerability arises from improper access control in the digital signature verification process of the firmware. In particular, the verification mechanism fails to properly validate variable attributes, enabling an attacker to create a non-authenticated NVRAM (Non-Volatile Random Access Memory) variable. This flaw allows an attacker to bypass the Secure Boot mechanism by executing arbitrary signed UEFI code without proper authentication. Secure Boot is a critical security feature designed to prevent unauthorized code from running during the system boot process, ensuring only trusted firmware and software components are loaded. By exploiting this vulnerability, an attacker with low privileges but local access could escalate their control by injecting malicious code into the boot sequence, compromising the system's integrity and potentially gaining persistent, stealthy control over the device. The CVSS 3.1 score of 7.8 reflects the high impact on confidentiality, integrity, and availability, with the attack vector being local and requiring high attack complexity but only low privileges and no user interaction. The vulnerability's scope is significant as it affects the firmware layer, which underpins the entire operating system and security posture of affected devices. No known exploits are currently reported in the wild, and no patches have been linked yet, indicating that mitigation may rely on vendor updates once available and interim security controls.

For European organizations, the impact of CVE-2025-4275 is substantial. Compromise at the UEFI firmware level undermines foundational system security, enabling attackers to bypass Secure Boot protections and persist undetected through reboots and OS reinstalls. This can lead to full system compromise, data breaches, intellectual property theft, and disruption of critical services. Organizations in sectors such as finance, healthcare, government, and critical infrastructure are particularly at risk due to the sensitive nature of their data and the high value of maintaining system integrity. The ability to execute arbitrary signed UEFI code could facilitate advanced persistent threats (APTs), supply chain attacks, or ransomware campaigns with firmware-level persistence. Given the local attack vector, insider threats or attackers with physical or limited remote access could exploit this vulnerability. The lack of user interaction required increases the risk of automated or stealthy exploitation once access is gained. European organizations relying on hardware with InsydeH2O firmware versions 5.2 to 5.7 should consider this a critical risk to their endpoint and server security.

1. Immediate inventory and identification of all systems running InsydeH2O firmware versions 5.2 through 5.7 is essential. 2. Monitor Insyde Software and hardware vendors for official security patches or firmware updates addressing CVE-2025-4275 and apply them promptly upon release. 3. Implement strict physical security controls to limit unauthorized local access to systems, as exploitation requires local access. 4. Employ endpoint detection and response (EDR) tools capable of monitoring firmware-level anomalies and suspicious boot-time activities. 5. Use hardware-based security features such as TPM (Trusted Platform Module) and enable measured boot where possible to detect unauthorized firmware modifications. 6. Restrict and monitor administrative privileges to reduce the risk of privilege escalation that could facilitate exploitation. 7. Conduct regular firmware integrity checks and audits to detect unauthorized changes to NVRAM variables or boot configurations. 8. Educate IT and security teams about the risks of firmware-level attacks and ensure incident response plans include firmware compromise scenarios. 9. Consider network segmentation to isolate critical systems and limit lateral movement if a device is compromised. 10. Maintain up-to-date backups and recovery procedures to restore systems in case of compromise.