CVE-2023-40250
📋 TL;DR
A classic buffer overflow vulnerability in Hancom HCell spreadsheet software allows attackers to execute arbitrary code by sending specially crafted input that exceeds buffer boundaries. This affects all Windows users running HCell version 12.0.0.893. Successful exploitation could lead to complete system compromise.
💻 Affected Systems
- Hancom HCell
📦 What is this software?
Hcell by Hancom
⚠️ Risk & Real-World Impact
Worst Case
Remote code execution with SYSTEM privileges leading to complete host takeover, data exfiltration, and lateral movement within the network.
Likely Case
Local privilege escalation or remote code execution in the context of the current user, potentially leading to malware installation or data theft.
If Mitigated
Application crash (denial of service) if exploit fails or memory protections prevent code execution.
🎯 Exploit Status
Requires user to open a malicious spreadsheet file; buffer overflow exploitation typically requires some technical skill but is well-understood.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Check vendor website for updated version
Vendor Advisory: https://www.hancom.com/cs_center/csDownload.do?gnb0=25gnb1=80
Restart Required: Yes
Instructions:
1. Visit the Hancom download center
2. Download the latest version of HCell
3. Install the update
4. Restart the system
🔧 Temporary Workarounds
Restrict file execution
windowsBlock execution of HCell files from untrusted sources using application control policies
Using AppLocker or Windows Defender Application Control: Create rule to block HCell execution from network shares, email attachments, or untrusted zones
Disable HCell file associations
windowsPrevent .cell files from automatically opening in HCell
reg add "HKEY_CLASSES_ROOT\.cell" /v "Content Type" /t REG_SZ /d "application/octet-stream" /f
🧯 If You Can't Patch
- Implement strict application whitelisting to prevent unauthorized HCell execution
- Use network segmentation to isolate systems running vulnerable HCell versions
🔍 How to Verify
Check if Vulnerable:
Check HCell version: Open HCell → Help → About HCell → Verify version is 12.0.0.893Check Version:
wmic product where "name like 'Hancom%HCell%'" get versionVerify Fix Applied:
After update, verify version is no longer 12.0.0.893 and matches latest version from vendor site📡 Detection & Monitoring
Log Indicators:
- Application crashes of HCell.exe with exception codes like 0xC0000005 (ACCESS_VIOLATION)
- Unusual process creation from HCell.exe
Network Indicators:
- Downloads of .cell files from untrusted sources
- Outbound connections from HCell.exe to suspicious IPs
SIEM Query:
Process:Name='HCell.exe' AND (EventID=1000 OR EventID=1001) AND ExceptionCode=0xC0000005