CVE-2020-8740: Intel BIOS Privilege Escalation Flaw

CVE-2020-8740 Overview

CVE-2020-8740 is an out-of-bounds write vulnerability in Intel BIOS platform sample code that affects a wide range of Intel processors, including Intel Core i5, i7, i9, and Xeon processor families. This firmware-level vulnerability allows a privileged user to potentially escalate their privileges through local access to the system. The vulnerability exists in the BIOS reference code provided by Intel that OEMs use to develop their own BIOS implementations.

Critical Impact

A privileged attacker with local access can exploit the out-of-bounds write condition in the BIOS firmware to gain elevated privileges, potentially compromising the entire system at a foundational level that persists across operating system reinstallations.

Affected Products

• Intel BIOS platform sample code
• Intel Core i5-7640X, Core i7 (3rd-10th Gen X-series), Core i9 (7th-10th Gen X-series) Processors
• Intel Xeon Bronze, Silver, Gold, Platinum, W-series, D-series, E5, and E7 Processors
• NetApp AFF, FAS, HCI Compute Node, HCI Storage Node, and SolidFire BIOS

Discovery Timeline

• November 12, 2020 - CVE-2020-8740 published to NVD
• November 21, 2024 - Last updated in NVD database

Technical Details for CVE-2020-8740

Vulnerability Analysis

This vulnerability is classified as CWE-787 (Out-of-bounds Write), a memory corruption flaw that occurs when the BIOS platform sample code writes data past the boundaries of an allocated memory buffer. The vulnerability requires local access and high privileges to exploit, but successful exploitation can result in complete compromise of system confidentiality, integrity, and availability.

The firmware-level nature of this vulnerability makes it particularly concerning because BIOS/UEFI code executes before the operating system loads, operating at the highest privilege level (Ring -2). An attacker who successfully exploits this vulnerability could establish persistent access that survives operating system reinstallation, install firmware-level rootkits, or disable security features like Secure Boot.

Root Cause

The root cause is improper bounds checking in Intel's BIOS platform sample code. When processing certain inputs or data structures, the code fails to properly validate the size or boundaries of data being written to memory buffers. This allows an attacker to craft malicious inputs that cause writes beyond the intended memory region, potentially overwriting critical firmware data structures or code.

Attack Vector

The attack requires local access to the affected system and elevated privileges. An attacker would need to be able to interact with the BIOS/UEFI environment directly, either through operating system interfaces that communicate with firmware (such as UEFI runtime services), or through direct access to the pre-boot environment. The exploitation scenario typically involves:

1. Gaining privileged access to the target system (administrator/root level)
2. Identifying the vulnerable BIOS implementation on the target hardware
3. Crafting specially formatted data that triggers the out-of-bounds write condition
4. Leveraging the memory corruption to execute arbitrary code at the firmware level or modify critical security configurations

The vulnerability affects systems using Intel BIOS platform sample code, which serves as reference implementation for OEM BIOS developers. This means the actual impact depends on how individual OEMs incorporated this code into their specific BIOS implementations.

Detection Methods for CVE-2020-8740

Indicators of Compromise

• Unexpected modifications to BIOS/UEFI firmware settings or code sections
• Firmware integrity check failures during Secure Boot validation
• Anomalous behavior during system boot sequence or POST (Power-On Self-Test)
• Unauthorized changes to boot configuration that persist after operating system reinstallation

Detection Strategies

• Implement hardware-based firmware attestation using TPM (Trusted Platform Module) to detect unauthorized firmware modifications
• Deploy endpoint detection solutions capable of monitoring UEFI runtime service calls for suspicious activity
• Utilize Intel's own firmware verification tools to check BIOS integrity against known-good baselines
• Monitor for privileged users attempting to access firmware update mechanisms or UEFI variables

Monitoring Recommendations

• Enable and monitor Secure Boot status and violations across all affected systems
• Configure alerts for any firmware update activities outside of scheduled maintenance windows
• Implement centralized logging of BIOS/UEFI events where supported by hardware management interfaces
• Regularly perform firmware integrity verification using vendor-provided tools or third-party firmware scanning solutions

How to Mitigate CVE-2020-8740

Immediate Actions Required

• Apply BIOS/UEFI firmware updates from your system OEM that incorporate Intel's fixes for this vulnerability
• Restrict physical access to affected systems and limit the number of users with administrative privileges
• Enable Secure Boot and configure BIOS passwords to prevent unauthorized firmware modifications
• Review and harden all systems with affected Intel processors, particularly servers and workstations in critical environments

Patch Information

Intel has addressed this vulnerability in updated BIOS platform sample code provided to OEMs. Organizations should obtain firmware updates directly from their system or motherboard manufacturer (Dell, HP, Lenovo, Supermicro, etc.) rather than from Intel directly. Refer to Intel Security Advisory INTEL-SA-00390 for detailed information about the vulnerability and affected products. NetApp customers should also review the NetApp Security Advisory NTAP-20210122-0008 for guidance on affected NetApp systems.

Workarounds

• Implement strict access controls to limit who can access systems with administrative or root privileges
• Enable and enforce Secure Boot with custom keys where possible to detect unauthorized firmware modifications
• Use hardware security features such as Intel Boot Guard where available to protect against firmware-level attacks
• Isolate critical systems that cannot be immediately patched and monitor them closely for suspicious activity

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

# Check current BIOS version (compare against vendor advisories)
dmidecode -s bios-version

# View UEFI variables for potential tampering indicators
efivar -l | grep -i boot