CVE-2021-33834
📋 TL;DR
This vulnerability in Insyde H2OFFT's iscflashx64.sys driver allows attackers to cause memory corruption or system crashes by sending a malformed IOCTL request. It affects systems running Insyde firmware with the vulnerable driver version. Attackers could potentially escalate privileges or cause denial of service.
💻 Affected Systems
- Insyde H2OFFT firmware
📦 What is this software?
H2offt by Insyde
⚠️ Risk & Real-World Impact
Worst Case
Kernel-level privilege escalation leading to full system compromise, arbitrary code execution, or permanent system instability requiring hardware replacement.
Likely Case
System crash (BSOD) causing denial of service, potentially requiring physical intervention to restart affected systems.
If Mitigated
Limited to denial of service if proper access controls prevent unauthorized users from making IOCTL calls to the driver.
🎯 Exploit Status
Exploitation requires ability to send IOCTL requests to the driver, which typically requires some level of system access. No public exploit code has been identified.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Check with OEM for updated firmware versions
Vendor Advisory: https://www.insyde.com/security-pledge/SA-2021004
Restart Required: Yes
Instructions:
1. Contact your device manufacturer for updated firmware. 2. Download and install the firmware update. 3. Reboot the system to apply the update. 4. Verify the driver version is no longer 3.9.3.0.
🔧 Temporary Workarounds
Restrict driver access
windowsModify permissions to prevent non-administrative users from accessing the vulnerable driver
icacls C:\Windows\System32\drivers\iscflashx64.sys /deny Users:(R,X)
icacls C:\Windows\System32\drivers\iscflashx64.sys /deny Everyone:(R,X)
Disable driver
windowsPrevent the vulnerable driver from loading at system startup
sc config iscflashx64 start= disabled
sc stop iscflashx64
🧯 If You Can't Patch
- Implement strict access controls to prevent unauthorized users from executing code on affected systems
- Monitor for system crashes or unusual driver activity that might indicate exploitation attempts
🔍 How to Verify
Check if Vulnerable:
Check driver version: Open Device Manager, find 'Insyde Flash' under System devices, check Properties > Driver tab for version 3.9.3.0Check Version:
driverquery /v | findstr /i iscflashx64Verify Fix Applied:
Verify driver version is updated to a version other than 3.9.3.0 in Device Manager📡 Detection & Monitoring
Log Indicators:
- System crash logs (Event ID 41)
- Driver load failures
- Access denied errors for iscflashx64.sys
Network Indicators:
- No network indicators - this is a local vulnerability
SIEM Query:
EventID=41 AND Source='Microsoft-Windows-Kernel-Power' OR (ProcessName='*' AND CommandLine LIKE '%iscflashx64%')