CVE-2020-0591: Intel BIOS Privilege Escalation Flaw

CVE-2020-0591 Overview

CVE-2020-0591 is a firmware-level vulnerability affecting the BIOS of numerous Intel processors, including Xeon, Core i5, Core i7, and Core i9 product families. The vulnerability stems from improper buffer restrictions within the BIOS firmware, which may allow a privileged user with local access to escalate their privileges on the affected system. This BIOS/UEFI vulnerability poses significant risks to enterprise environments, data centers, and industrial control systems utilizing affected Intel processors.

Critical Impact

A privileged attacker with local access can exploit improper buffer restrictions in Intel BIOS firmware to achieve privilege escalation, potentially gaining higher-level system control and compromising the integrity of the entire system at the firmware level.

Affected Products

• Intel BIOS Firmware (multiple processor families)
• Intel Xeon Scalable Processors (Bronze, Silver, Gold, Platinum series)
• Intel Core X-series Processors (i5-7640X, i7, i9 families)
• Intel Xeon D-series Processors (D-1500, D-1600, D-2100 families)
• Intel Xeon W-series Processors (W-1200, W-2200, W-3200 families)
• Siemens SIMATIC CPU 1518-4 and 1518F-4 Firmware

Discovery Timeline

• November 12, 2020 - CVE-2020-0591 published to NVD
• November 21, 2024 - Last updated in NVD database

Technical Details for CVE-2020-0591

Vulnerability Analysis

This vulnerability exists within the BIOS firmware layer, which operates at System Management Mode (SMM) privilege level—the highest privilege level in x86 architecture. The improper buffer restrictions create a condition where memory operations within the BIOS code fail to properly validate or constrain data boundaries. When exploited by an attacker who already possesses elevated privileges on the system, this flaw can be leveraged to achieve further privilege escalation, potentially allowing code execution within the SMM context.

The exploitation requires local access and an already-privileged position, which limits the attack surface to insider threats or scenarios where an attacker has already compromised a user account with administrative capabilities. However, successful exploitation at the BIOS/firmware level is particularly dangerous because it operates below the operating system, making detection extremely difficult and persistence highly effective.

Root Cause

The root cause of CVE-2020-0591 is improper buffer restrictions within the Intel BIOS firmware code. This occurs when the firmware fails to adequately validate the size or boundaries of data being written to or read from memory buffers. In firmware contexts, such buffer management issues can allow data to overflow into adjacent memory regions, potentially corrupting critical system structures or allowing arbitrary code execution in the highly privileged SMM environment.

Attack Vector

The attack vector for this vulnerability is local, requiring an attacker to have physical or logical access to the target system. The attacker must already possess high privileges (administrative or root-level access) on the host operating system. From this position, the attacker can interact with the BIOS firmware through mechanisms such as UEFI runtime services, System Management Interrupt (SMI) handlers, or direct memory access to BIOS regions. By crafting malicious input that exceeds the expected buffer boundaries, the attacker can potentially corrupt memory, hijack execution flow, or inject malicious code that executes with SMM privileges.

Due to the firmware-level nature of this vulnerability and the absence of verified proof-of-concept code, technical implementation details are not publicly available. Organizations should consult the Intel Security Advisory SA-00358 for comprehensive technical guidance.

Detection Methods for CVE-2020-0591

Indicators of Compromise

• Unexpected modifications to BIOS/UEFI firmware or firmware version discrepancies
• Anomalous System Management Interrupt (SMI) activity or frequency
• Unauthorized changes to Secure Boot configuration or disabled security features
• Evidence of privilege escalation from admin-level to firmware-level persistence

Detection Strategies

• Deploy firmware integrity monitoring solutions that verify BIOS/UEFI code against known-good baselines
• Implement endpoint detection and response (EDR) solutions capable of monitoring for firmware-level anomalies
• Use hardware-based attestation mechanisms (Intel TXT, TPM) to verify platform integrity at boot
• Monitor for unusual access patterns to UEFI runtime services or SMI handlers

Monitoring Recommendations

• Enable and review BIOS/UEFI event logging for unauthorized access attempts or configuration changes
• Implement SentinelOne's firmware protection capabilities to detect tampering at the pre-boot level
• Conduct regular firmware version audits across enterprise systems to identify unpatched devices
• Establish baseline firmware configurations and alert on any deviations

How to Mitigate CVE-2020-0591

Immediate Actions Required

• Identify all systems using affected Intel processors and prioritize them for firmware updates
• Apply the latest BIOS/UEFI firmware updates from your system OEM or motherboard manufacturer
• Restrict local administrative access to minimize the pool of potential attackers
• Enable Secure Boot and configure BIOS passwords to prevent unauthorized firmware modifications

Patch Information

Intel has released updated BIOS firmware to address this vulnerability. Organizations should obtain patched firmware from their respective system manufacturers (OEMs) or motherboard vendors, as Intel does not distribute BIOS updates directly to end users. Refer to the Intel Security Advisory SA-00358 for the complete list of affected products and remediation guidance.

For Siemens SIMATIC CPU 1518-4 and 1518F-4 devices, consult the Siemens Security Advisory SSA-501073 for specific patch information and mitigation guidance applicable to industrial control system environments.

Workarounds

• Implement strict physical security controls to limit local access to affected systems
• Enforce the principle of least privilege to minimize the number of users with administrative access
• Enable BIOS write protection features where available to prevent unauthorized firmware modifications
• Deploy additional monitoring for privileged account activity and firmware access attempts

# Example: Check current BIOS version on Linux systems
sudo dmidecode -s bios-version
sudo dmidecode -t bios | grep -i "version\|release"

# Verify Secure Boot status
mokutil --sb-state