CVE-2021-33122: Intel Xeon E-2386g Privilege Escalation

CVE-2021-33122 Overview

CVE-2021-33122 is a privilege escalation vulnerability affecting the BIOS firmware of numerous Intel processors. The vulnerability stems from insufficient control flow management within the BIOS firmware, which may allow a privileged user with local access to escalate their privileges on the affected system. This firmware-level vulnerability impacts a wide range of Intel processor families including Core i3, i5, i7, i9, Xeon E, Xeon W, Pentium Silver, and Celeron processors spanning 9th through 12th generation architectures.

Critical Impact

A privileged attacker with local access can exploit this BIOS firmware vulnerability to escalate privileges, potentially gaining deeper system control and bypassing security boundaries at the firmware level.

Affected Products

• Intel Xeon E-series processors (E-2314, E-2324G, E-2334, E-2336, E-2356G, E-2374G, E-2378, E-2378G, E-2386G, E-2388G) and their firmware
• Intel Xeon W-series processors (W-1350, W-1350P, W-1370, W-1370P, W-1390, W-1390P, W-1390T) and their firmware
• Intel Core i3, i5, i7, i9 processors (9th, 10th, 11th, and 12th generation) and their firmware
• Intel Pentium Silver (N6000, N6005) and Celeron (N4000, N4020, N4100, N4120, N4500, N4505, N5100, N5105) processors and their firmware

Discovery Timeline

• May 12, 2022 - CVE-2021-33122 published to NVD
• May 5, 2025 - Last updated in NVD database

Technical Details for CVE-2021-33122

Vulnerability Analysis

This vulnerability exists within the BIOS firmware of affected Intel processors due to insufficient control flow management. The BIOS firmware, which executes during the early boot process before the operating system loads, contains code paths that do not properly enforce control flow integrity. This allows an attacker who already possesses elevated privileges on the system to manipulate execution flow within the BIOS context, potentially achieving even higher privilege levels or bypassing firmware security mechanisms.

The attack requires local access to the system, meaning the attacker must either have physical access or have already compromised the system to some degree. Once exploited, the attacker could gain persistent, low-level access that survives operating system reinstallation, as the compromise occurs at the firmware layer.

Root Cause

The root cause of CVE-2021-33122 is insufficient control flow management within the Intel BIOS firmware code. Control flow integrity is a security mechanism designed to ensure that program execution follows only legitimate paths through the code. When control flow management is insufficient, attackers can redirect execution to unintended code locations, potentially bypassing security checks or executing privileged operations.

In this case, the BIOS firmware lacks adequate enforcement of control flow constraints, allowing a privileged attacker to manipulate the execution path during firmware operations. This deficiency in the firmware's security architecture creates an avenue for privilege escalation.

Attack Vector

The attack vector for this vulnerability is local, requiring an attacker to have existing privileged access to the target system. The exploitation path involves manipulating the BIOS firmware's control flow during system operation or boot sequence. Since the vulnerability exists in firmware code, successful exploitation could:

• Allow escalation from operating system administrator to firmware-level control
• Enable persistent implants that survive OS reinstallation
• Bypass Secure Boot and other firmware-level security mechanisms
• Provide a foundation for rootkit installation below the OS level

The local access requirement and need for initial privileged access reduces the attack surface, but the potential for firmware-level persistence makes this a significant concern for high-security environments.

Detection Methods for CVE-2021-33122

Indicators of Compromise

• Unexpected BIOS/UEFI configuration changes or modifications to firmware settings
• Anomalous system behavior during boot sequences or POST operations
• Firmware integrity check failures reported by hardware security modules or TPM
• Unexplained persistence of malware or unauthorized code after complete system reimaging

Detection Strategies

• Implement firmware integrity monitoring using Intel Boot Guard or similar trusted computing technologies
• Deploy endpoint detection solutions capable of monitoring BIOS/UEFI interactions and firmware access patterns
• Utilize hardware security module (HSM) or TPM-based attestation to verify firmware integrity at boot time
• Monitor for unauthorized BIOS update attempts or firmware modification activities in system logs

Monitoring Recommendations

• Enable and regularly review BIOS/UEFI event logs for suspicious modification attempts
• Implement Secure Boot with custom keys to detect unauthorized firmware changes
• Use enterprise firmware management solutions to track BIOS versions and detect unauthorized updates
• Deploy SentinelOne agents configured to monitor for firmware-level anomalies and boot process irregularities

How to Mitigate CVE-2021-33122

Immediate Actions Required

• Inventory all systems using affected Intel processors to determine exposure scope
• Apply the latest BIOS/UEFI firmware updates from your system or motherboard manufacturer
• Enable Secure Boot and configure firmware passwords to restrict unauthorized BIOS access
• Restrict physical access to affected systems and implement strong local privilege controls

Patch Information

Intel has released updated BIOS firmware to address this vulnerability. Organizations should obtain the appropriate firmware updates from their system manufacturer (OEM), as BIOS updates are typically distributed through the hardware vendor rather than directly from Intel. Consult the Intel Security Advisory SA-00601 for detailed information on affected processor families and recommended mitigation steps. Additionally, refer to the NetApp Security Advisory NTAP-20220818-0003 for information on affected NetApp products.

Workarounds

• Implement strict access controls to limit which users can access BIOS/UEFI settings and perform firmware updates
• Enable Intel Boot Guard where supported to establish a hardware root of trust
• Configure firmware passwords and disable unnecessary boot options to reduce attack surface
• For systems where patching is not immediately possible, increase monitoring and restrict local administrative access

# Example: Check current BIOS version on Linux systems
sudo dmidecode -s bios-version
sudo dmidecode -s bios-release-date

# Verify Intel processor model
lscpu | grep "Model name"

# Check for Secure Boot status
mokutil --sb-state