CVE-2025-20027: Intel UEFI Privilege Escalation Flaw

CVE-2025-20027 Overview

CVE-2025-20027 is an improper input validation vulnerability in the UEFI WheaERST (Windows Hardware Error Architecture Error Record Serialization Table) module affecting some Intel reference platforms. This BIOS/UEFI vulnerability allows a privileged local attacker to escalate privileges on vulnerable systems through manipulation of firmware-level components.

The WheaERST module is responsible for persisting hardware error records across system reboots, providing critical diagnostic information for system reliability. When input validation is improperly implemented in this module, attackers with existing elevated privileges can potentially bypass firmware security boundaries and achieve deeper system compromise.

Critical Impact

Local privilege escalation vulnerability in Intel UEFI firmware allows attackers with privileged access to compromise system confidentiality, integrity, and availability at the firmware level.

Affected Products

• Intel reference platforms with vulnerable UEFI WheaERST module implementations
• Systems using affected Intel firmware reference code
• OEM systems derived from vulnerable Intel reference BIOS implementations

Discovery Timeline

• 2026-03-10 - CVE-2025-20027 published to NVD
• 2026-03-11 - Last updated in NVD database

Technical Details for CVE-2025-20027

Vulnerability Analysis

This vulnerability stems from improper input validation (CWE-20) within the UEFI WheaERST module. The WheaERST component handles hardware error record persistence, interfacing between the operating system and non-volatile storage to maintain error logs across power cycles.

The vulnerability requires a complex attack scenario: an adversary must already possess privileged user access to the system and meet specific attack requirements for successful exploitation. The attack vector is local, meaning physical or authenticated local access to the system is required—remote exploitation is not possible.

When successfully exploited, the vulnerability can result in complete compromise of confidentiality, integrity, and availability of the vulnerable system at the firmware level. However, the scope is limited to the vulnerable component itself, with no direct impact propagating to subsequent systems or components.

Root Cause

The root cause is classified as CWE-20 (Improper Input Validation). The WheaERST module fails to adequately validate input parameters before processing them, allowing malformed or malicious input to trigger unintended behavior. In UEFI firmware, such validation failures are particularly dangerous as they operate below the operating system's security controls and can persist across reboots.

Input validation errors in firmware modules can allow attackers to:

• Write to protected memory regions
• Manipulate firmware variables
• Bypass Secure Boot protections
• Achieve persistent compromise that survives OS reinstallation

Attack Vector

The attack requires local access to the system with an already-privileged user account. The complexity is high, requiring specific attack prerequisites to be present. No user interaction is needed once the attacker has established their privileged position.

The attacker would typically interact with the WheaERST module through system management interfaces, ACPI tables, or direct firmware variable manipulation. By providing specially crafted input that bypasses validation checks, the attacker can trigger the privilege escalation condition.

For technical details on the vulnerability mechanism and affected firmware versions, refer to the Intel Security Advisory SA-01234.

Detection Methods for CVE-2025-20027

Indicators of Compromise

• Unexpected modifications to UEFI firmware variables related to WHEA or error logging
• Anomalous access patterns to System Management Mode (SMM) or firmware interfaces
• Changes to Secure Boot configuration or firmware integrity measurements
• Suspicious activity from privileged processes interacting with ACPI or firmware management interfaces

Detection Strategies

• Monitor for unexpected firmware variable modifications using platform security tools
• Implement firmware integrity monitoring to detect unauthorized changes to UEFI modules
• Enable and review Trusted Platform Module (TPM) event logs for anomalous firmware measurements
• Deploy endpoint detection solutions capable of monitoring privileged operations targeting firmware interfaces

Monitoring Recommendations

• Enable firmware event logging through platform security features where available
• Regularly verify firmware integrity using vendor-provided validation tools
• Monitor system event logs for WHEA-related errors or unexpected firmware interactions
• Implement hardware security module (HSM) or TPM-based attestation for boot integrity verification

How to Mitigate CVE-2025-20027

Immediate Actions Required

• Review the Intel Security Advisory SA-01234 for affected firmware versions
• Contact your system OEM for BIOS/UEFI updates that address this vulnerability
• Restrict local privileged access to affected systems to minimize exposure
• Enable Secure Boot and ensure firmware write protections are active where supported

Patch Information

Intel has published security guidance through Intel Security Advisory SA-01234. System administrators should consult their OEM vendor for specific BIOS/UEFI updates, as Intel reference platform code is typically customized by hardware manufacturers before deployment.

Firmware updates should be applied through the system vendor's official update channels. Verify firmware update authenticity before installation using cryptographic signatures where available.

Workarounds

• Implement strict access controls to limit privileged local access to affected systems
• Enable UEFI Secure Boot to provide additional firmware integrity protections
• Configure BIOS/UEFI write protection features if available on your platform
• Isolate affected systems from untrusted users until patches are applied
• Monitor privileged account activity for suspicious firmware-related operations

# Verify Secure Boot status on Linux systems
mokutil --sb-state

# Check UEFI firmware variables (requires root)
efivar -l | grep -i whea

# Verify TPM measurements for firmware integrity
tpm2_eventlog /sys/kernel/security/tpm0/binary_bios_measurements