CVE-2025-20064: Intel UEFI Privilege Escalation Flaw

CVE-2025-20064 Overview

CVE-2025-20064 is a BIOS/UEFI vulnerability affecting Intel reference platforms through improper input validation in the UEFI FlashUcAcmSmm module. This security flaw allows a privileged local attacker to escalate privileges and achieve local code execution on vulnerable systems. The vulnerability resides in System Management Mode (SMM) firmware, a highly privileged execution environment that operates below the operating system level.

Critical Impact

Successful exploitation enables local code execution with elevated privileges, potentially compromising system confidentiality, integrity, and availability at both the initial system level and subsequent system operations.

Affected Products

• Intel reference platforms with vulnerable UEFI FlashUcAcmSmm module
• Systems utilizing affected Intel BIOS/UEFI firmware implementations
• OEM systems based on vulnerable Intel reference platform designs

Discovery Timeline

• 2026-03-10 - CVE-2025-20064 published to NVD
• 2026-03-11 - Last updated in NVD database

Technical Details for CVE-2025-20064

Vulnerability Analysis

This vulnerability stems from improper input validation (CWE-20) within the FlashUcAcmSmm UEFI module. The SMM handler fails to properly validate input parameters before processing, creating an opportunity for privilege escalation. SMM operates in a ring -2 privilege level, making it one of the most privileged execution contexts on x86 systems—even more privileged than the hypervisor or operating system kernel.

The attack requires local access and elevated privileges (such as administrator or root), combined with high attack complexity. While these prerequisites raise the bar for exploitation, successful attacks can have devastating consequences given SMM's position in the system trust hierarchy. An attacker who compromises SMM can potentially bypass security controls, install persistent malware that survives OS reinstallation, or disable security features.

Root Cause

The root cause is improper input validation in the FlashUcAcmSmm SMM handler. When the SMM interrupt (SMI) is triggered, the handler processes input parameters without adequate boundary checking or sanitization. This allows a privileged attacker to supply crafted input that escapes intended constraints, leading to unauthorized code execution within the SMM context.

The FlashUcAcmSmm module is responsible for flash memory operations related to Authenticated Code Module (ACM) updates. The failure to validate inputs in this security-critical module creates a pathway for attackers to manipulate flash operations or execute arbitrary code in SMM.

Attack Vector

The attack vector is local, requiring the adversary to have existing privileged access to the system. The attacker must be able to trigger SMI handlers and supply malicious input to the vulnerable FlashUcAcmSmm module. While no user interaction is required, the attack complexity is high, indicating that specific conditions or timing may be necessary for successful exploitation.

A typical attack scenario would involve:

1. Gaining local privileged access to the target system
2. Identifying the vulnerable SMM handler entry point
3. Crafting malicious input parameters to exploit the validation flaw
4. Triggering the SMI to invoke the vulnerable handler
5. Achieving code execution in SMM context, enabling persistent compromise

The vulnerability does not require special internal knowledge of the system and can be exploited when standard attack requirements are met.

Detection Methods for CVE-2025-20064

Indicators of Compromise

• Unexpected SMI activity or anomalous SMM handler invocations
• Unauthorized modifications to UEFI firmware or flash memory regions
• Suspicious processes attempting to interact with low-level system management interfaces
• Evidence of privilege escalation from user-mode to kernel or SMM contexts

Detection Strategies

• Deploy endpoint detection and response (EDR) solutions capable of monitoring firmware-level activity
• Implement UEFI integrity verification using measured boot and attestation mechanisms
• Monitor for processes attempting to trigger SMI handlers or access SMM-related interfaces
• Use hardware security modules or trusted platform modules (TPM) to detect unauthorized firmware modifications

Monitoring Recommendations

• Enable secure boot and verify firmware signatures during each boot cycle
• Implement continuous firmware integrity monitoring using vendor-provided or third-party tools
• Review system event logs for unusual privilege escalation attempts or SMI-related activity
• Establish baseline firmware hashes and alert on any deviations

How to Mitigate CVE-2025-20064

Immediate Actions Required

• Review the Intel Security Advisory for specific patching guidance
• Contact your OEM vendor to obtain updated BIOS/UEFI firmware that addresses this vulnerability
• Restrict local administrative access to systems pending firmware updates
• Enable Secure Boot and ensure firmware write protections are active where available

Patch Information

Intel has released security guidance through their advisory process. Organizations should consult the Intel Security Advisory for detailed patch information and coordinate with their OEM vendors to obtain updated BIOS/UEFI firmware packages. Due to the nature of UEFI vulnerabilities, patches are typically distributed through system manufacturers rather than directly from Intel.

Workarounds

• Limit local privileged access to affected systems to trusted administrators only
• Enable UEFI Secure Boot and configure firmware write protection where supported
• Implement additional monitoring for SMI activity and firmware integrity
• Consider network segmentation to limit exposure of affected systems until patches are applied

Firmware update procedures vary by system manufacturer. The following represents a general approach—consult your OEM documentation for specific instructions:

# General firmware update verification approach
# Check current BIOS version
dmidecode -s bios-version

# Verify firmware integrity using vendor tools
# Example: Check if Secure Boot is enabled
mokutil --sb-state

# Monitor for SMI activity (requires specialized tools)
# Contact your security vendor for SMM monitoring capabilities