CVE-2021-42554: Insyde InsydeH2O Privilege Escalation Flaw

CVE-2021-42554 Overview

CVE-2021-42554 is a critical SMM (System Management Mode) memory corruption vulnerability discovered in Insyde InsydeH2O UEFI firmware. The vulnerability exists in the FvbServicesRuntimeDxe driver and allows an attacker with high privileges to write fixed or predictable data to SMRAM (System Management RAM). Successful exploitation of this vulnerability could lead to privilege escalation to SMM, which represents the highest privilege level in x86 architecture.

This BIOS/UEFI vulnerability affects multiple versions of Insyde InsydeH2O firmware including Kernel 5.0 before 05.08.42, Kernel 5.1 before 05.16.42, Kernel 5.2 before 05.26.42, Kernel 5.3 before 05.35.42, Kernel 5.4 before 05.42.51, and Kernel 5.5 before 05.50.51. The widespread use of InsydeH2O firmware across multiple OEM vendors means this vulnerability impacts a broad range of enterprise and industrial computing devices.

Critical Impact

Successful exploitation allows attackers to escalate privileges to SMM, enabling persistent firmware-level compromise that survives OS reinstallation and can bypass security controls.

Affected Products

• Insyde InsydeH2O (Kernel 5.0 - 5.5 various versions)
• Siemens SIMATIC Field PG M5/M6 Firmware
• Siemens SIMATIC IPC127E, IPC227G, IPC277G, IPC327G, IPC377G Firmware
• Siemens SIMATIC IPC427E, IPC477E, IPC627E, IPC647E, IPC677E, IPC847E Firmware
• Siemens SIMATIC ITP1000 Firmware
• Siemens RUGGEDCOM APE1808 Firmware

Discovery Timeline

• February 3, 2022 - CVE-2021-42554 published to NVD
• November 4, 2025 - Last updated in NVD database

Technical Details for CVE-2021-42554

Vulnerability Analysis

This vulnerability is classified as CWE-787 (Out-of-Bounds Write), indicating that the FvbServicesRuntimeDxe driver improperly validates memory boundaries when writing data. The flaw allows an attacker with local access and high privileges to corrupt SMM memory regions. SMM operates at a higher privilege level than the operating system kernel, making this a particularly dangerous class of vulnerability.

The attack requires local access and high privileges to execute, but the impact scope extends beyond the vulnerable component. An attacker who successfully exploits this vulnerability gains the ability to execute arbitrary code in SMM context, potentially allowing them to install persistent firmware implants, bypass Secure Boot protections, and maintain stealthy access that cannot be removed through normal OS-level remediation.

Root Cause

The root cause of CVE-2021-42554 lies in improper input validation within the FvbServicesRuntimeDxe (Firmware Volume Block Services Runtime DXE) driver. This driver is responsible for providing runtime services for firmware volume block operations during the UEFI boot process. The vulnerability allows fixed or predictable data to be written to SMRAM regions due to insufficient boundary checks on memory write operations.

Attack Vector

The attack vector for this vulnerability is local, requiring the attacker to have already obtained high-privileged access to the target system. The exploitation chain typically involves:

1. Gaining administrative or root access to the target operating system
2. Leveraging OS-level capabilities to interact with UEFI runtime services
3. Crafting malicious input to trigger the out-of-bounds write in FvbServicesRuntimeDxe
4. Writing controlled data to SMRAM to corrupt SMM handler code or data
5. Triggering an SMI (System Management Interrupt) to execute the corrupted SMM code

The vulnerability mechanism involves the firmware driver failing to properly validate buffer boundaries when processing firmware volume block operations. This allows an attacker to specify memory addresses or offsets that exceed the intended bounds, resulting in writes to protected SMRAM regions. For detailed technical analysis, refer to the CERT Vulnerability Report ID 796611 and the Insyde Security Advisory SA-2022012.

Detection Methods for CVE-2021-42554

Indicators of Compromise

• Unexpected modifications to UEFI firmware or BIOS settings that persist after restoration attempts
• Detection of unknown or unauthorized SMI handlers during firmware analysis
• Anomalous system behavior during boot that may indicate compromised firmware integrity
• Evidence of tools designed to interact with UEFI runtime services from user space

Detection Strategies

• Deploy firmware integrity monitoring solutions capable of validating UEFI firmware against known-good baselines
• Utilize hardware security modules (TPM) to measure and attest firmware state during boot
• Monitor for suspicious access patterns to UEFI runtime services from privileged OS contexts
• Implement endpoint detection solutions with visibility into low-level system interactions

Monitoring Recommendations

• Enable UEFI Secure Boot with proper key management to detect unauthorized firmware modifications
• Periodically verify firmware versions against vendor-published secure versions
• Monitor system event logs for unexpected SMI activity or UEFI-related errors
• Implement SentinelOne Singularity platform for comprehensive endpoint visibility including firmware-level threat detection

How to Mitigate CVE-2021-42554

Immediate Actions Required

• Identify all systems running affected Insyde InsydeH2O firmware versions and prioritize patching
• Apply firmware updates from device OEMs that incorporate Insyde's security fixes
• Restrict administrative access to potentially affected systems pending firmware updates
• Enable UEFI Secure Boot if not already configured to provide additional protection layers

Patch Information

Insyde has released patched firmware versions to address this vulnerability. Organizations should apply the following minimum versions:

• Kernel 5.0: Update to version 05.08.42 or later
• Kernel 5.1: Update to version 05.16.42 or later
• Kernel 5.2: Update to version 05.26.42 or later
• Kernel 5.3: Update to version 05.35.42 or later
• Kernel 5.4: Update to version 05.42.51 or later
• Kernel 5.5: Update to version 05.50.51 or later

For Siemens industrial devices, consult the Siemens Security Advisory SSA-306654 for device-specific update guidance. Additional vendor-specific information is available through the NetApp Security Advisory NTAP-20220216-0007.

Workarounds

• Implement strict access controls to limit local administrative access to affected systems
• Enable hardware-based security features such as Intel Boot Guard where available
• Deploy application control policies to restrict execution of unknown binaries with elevated privileges
• Consider network segmentation to isolate affected systems until firmware updates can be applied

# Verify current UEFI firmware version on Linux systems
sudo dmidecode -t bios | grep -E "Vendor|Version|Release"

# Check if Secure Boot is enabled
mokutil --sb-state

# Monitor for SMI activity (requires root)
sudo dmesg | grep -i smi