CVE-2021-41842
📋 TL;DR
This vulnerability in Insyde InsydeH2O UEFI firmware allows arbitrary code execution at SMM (System Management Mode) privilege level due to missing CommBuffer validation in the AtaLegacySmm SMI handler. Attackers with local access can exploit this to gain persistent firmware-level control. Affects systems running vulnerable InsydeH2O firmware versions across multiple kernel branches.
💻 Affected Systems
- Systems with Insyde InsydeH2O UEFI firmware
📦 What is this software?
Insydeh2o by Insyde
Insydeh2o by Insyde
Insydeh2o by Insyde
Insydeh2o by Insyde
Insydeh2o by Insyde
Insydeh2o by Insyde
⚠️ Risk & Real-World Impact
Worst Case
Complete system compromise with persistent firmware-level malware installation, allowing attackers to bypass all OS-level security controls and maintain persistence across OS reinstalls.
Likely Case
Local privilege escalation to SMM level, enabling attackers to disable security features, install rootkits, or exfiltrate sensitive data from protected memory regions.
If Mitigated
Limited impact if proper firmware integrity verification and secure boot are enforced, though exploitation may still be possible with physical access or administrative privileges.
🎯 Exploit Status
Requires local access and ability to trigger SMI; exploitation requires understanding of SMM programming and firmware internals.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Kernel 5.0 05.08.46+, 5.1 05.16.46+, 5.2 05.26.46+, 5.3 05.35.46+, 5.4 05.43.46+, 5.5 05.51.45+
Vendor Advisory: https://www.insyde.com/security-pledge
Restart Required: Yes
Instructions:
1. Contact hardware manufacturer for firmware update. 2. Download appropriate firmware update from manufacturer's support site. 3. Follow manufacturer's firmware update procedure (typically involves bootable USB or Windows update utility). 4. Verify firmware version after update.
🔧 Temporary Workarounds
Enable Secure Boot
allSecure Boot helps prevent unauthorized firmware/OS modifications but doesn't directly patch the vulnerability
Restrict Physical Access
allLimit physical access to systems to reduce attack surface
🧯 If You Can't Patch
- Implement strict physical security controls and access monitoring
- Deploy endpoint detection and response (EDR) solutions to detect SMM exploitation attempts
🔍 How to Verify
Check if Vulnerable:
Check firmware version in UEFI/BIOS setup or using manufacturer-specific tools (e.g., dmidecode on Linux, msinfo32 on Windows)Check Version:
Linux: sudo dmidecode -t bios | grep Version; Windows: wmic bios get smbiosbiosversionVerify Fix Applied:
Verify firmware version matches or exceeds patched versions listed in affected_systems.versions📡 Detection & Monitoring
Log Indicators:
- Unexpected SMI triggers
- Firmware modification attempts in system logs
- Secure Boot violations
Network Indicators:
- Unusual outbound connections from firmware management interfaces
SIEM Query:
EventID=17 OR EventID=18 (Windows) for firmware events; look for unauthorized SMI calls