CVE-2025-4275: UEFI Secure Boot Bypass Vulnerability

CVE-2025-4275 Overview

A vulnerability exists in the digital signature verification process of UEFI firmware that fails to properly validate variable attributes. This security flaw allows an attacker to bypass signature verification by creating a non-authenticated NVRAM variable. Successful exploitation enables an attacker to execute arbitrary signed UEFI code and bypass Secure Boot protections, potentially compromising system integrity at the firmware level.

Critical Impact

Attackers can bypass Secure Boot protections by exploiting improper variable attribute validation in the digital signature verification process, enabling execution of arbitrary UEFI code and persistent firmware-level compromise.

Affected Products

• UEFI firmware implementations with affected digital signature verification
• Systems utilizing Insyde H2O UEFI firmware (refer to vendor advisory for specific versions)
• Enterprise and consumer devices with vulnerable BIOS/UEFI implementations

Discovery Timeline

• 2025-06-11 - CVE-2025-4275 published to NVD
• 2025-07-30 - Last updated in NVD database

Technical Details for CVE-2025-4275

Vulnerability Analysis

This vulnerability resides in the UEFI digital signature verification mechanism responsible for validating firmware components during the Secure Boot process. The flaw stems from inadequate validation of variable attributes when processing NVRAM variables, creating a pathway for attackers to circumvent cryptographic signature checks that would normally prevent unauthorized code execution.

The vulnerability requires local access and elevated privileges to exploit, but once successfully leveraged, it enables code execution within a changed security context. This represents a Secure Boot bypass vulnerability that undermines the fundamental trust chain designed to ensure only authenticated firmware and bootloaders execute during system startup.

An attacker who successfully exploits this vulnerability can install persistent malware at the firmware level, which survives operating system reinstallation and traditional security tools. This type of compromise is particularly dangerous as it provides attackers with stealth and persistence capabilities that are extremely difficult to detect and remediate.

Root Cause

The root cause of CVE-2025-4275 lies in improper input validation within the digital signature verification routine. Specifically, the firmware fails to adequately verify the attributes of NVRAM variables before trusting their contents for signature validation decisions. This allows an attacker to craft a malicious NVRAM variable that appears legitimate to the verification process but actually bypasses the intended security checks.

The lack of proper attribute validation means that variables without appropriate authentication requirements can influence the signature verification process, effectively allowing unsigned or improperly signed code to be treated as authenticated.

Attack Vector

The attack requires local access to the target system with low-level privileges. An attacker must be able to manipulate NVRAM variables, which typically requires either physical access or administrative privileges on the running operating system.

The exploitation process involves:

1. Creating a specially crafted NVRAM variable with attributes that bypass authentication checks
2. Leveraging this variable to influence the digital signature verification process
3. Loading and executing arbitrary UEFI code that would normally be blocked by Secure Boot
4. Establishing persistent firmware-level access that survives system reboots and OS reinstallation

The vulnerability enables attackers to execute arbitrary signed UEFI code, effectively neutralizing Secure Boot as a security control. This attack technique can be used to install bootkits, firmware implants, or other persistent threats.

Detection Methods for CVE-2025-4275

Indicators of Compromise

• Unexpected or unauthorized NVRAM variables present in UEFI variable storage
• Anomalous modifications to Secure Boot-related variables such as PK, KEK, db, or dbx
• Evidence of unsigned or improperly signed UEFI modules being loaded during boot
• Discrepancies in firmware integrity measurements reported by TPM or other attestation mechanisms

Detection Strategies

• Implement firmware integrity monitoring solutions that verify UEFI variable consistency
• Deploy endpoint detection and response (EDR) solutions with firmware-level visibility capabilities
• Enable and monitor TPM-based measured boot to detect unauthorized firmware modifications
• Conduct regular audits of NVRAM variable storage for unexpected entries or modifications

Monitoring Recommendations

• Enable UEFI audit logging where supported by firmware to track variable modifications
• Monitor for attempts to write to protected NVRAM storage areas
• Implement SentinelOne Singularity platform for comprehensive endpoint protection including firmware-level threat detection
• Establish baseline configurations for NVRAM variables and alert on deviations

How to Mitigate CVE-2025-4275

Immediate Actions Required

• Review the Insyde Security Advisory SA-2025002 for affected versions and available patches
• Consult the CERT Vulnerability Note VU#211341 for additional guidance and affected vendor information
• Contact your device manufacturer or OEM for firmware updates addressing this vulnerability
• Implement additional access controls to restrict NVRAM modification capabilities

Patch Information

Insyde has released security updates addressing this vulnerability. Organizations should consult the Insyde Security Advisory SA-2025002 for specific patch information and affected firmware versions. End users should contact their device manufacturers (OEMs) for updated BIOS/UEFI firmware that incorporates the fix.

Firmware updates typically require a system restart and may need to be applied through OEM-specific update utilities or UEFI update mechanisms. Organizations should test firmware updates in controlled environments before widespread deployment.

Workarounds

• Implement physical security controls to restrict unauthorized local access to systems
• Enable UEFI password protection to prevent unauthorized firmware configuration changes
• Deploy application whitelisting and enhanced access controls to limit who can modify NVRAM variables
• Consider enabling UEFI Secure Boot customization to implement organization-specific signing policies where supported
• Monitor systems with firmware-level visibility tools until patches can be applied