CVE-2021-44159
📋 TL;DR
This vulnerability allows unauthenticated remote attackers to upload arbitrary files, including webshells, to 4MOSAn GCB Doctor systems. Attackers can execute arbitrary code to perform system operations or denial-of-service attacks. All systems running vulnerable versions of 4MOSAn GCB Doctor are affected.
💻 Affected Systems
- 4MOSAn GCB Doctor
📦 What is this software?
⚠️ Risk & Real-World Impact
Worst Case
Complete system compromise allowing attackers to execute arbitrary commands, steal sensitive data, deploy ransomware, or disrupt critical healthcare operations.
Likely Case
Attackers upload webshells to gain persistent access, exfiltrate patient data, and use the system as a pivot point for lateral movement.
If Mitigated
With proper network segmentation and file upload restrictions, impact is limited to the specific application server.
🎯 Exploit Status
The vulnerability is straightforward to exploit - attackers simply need to craft a malicious file upload request without authentication.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Check with 4MOSAn for specific patched version
Vendor Advisory: https://www.twcert.org.tw/tw/cp-132-5395-eee40-1.html
Restart Required: Yes
Instructions:
1. Contact 4MOSAn for the security patch. 2. Apply the patch to all affected GCB Doctor installations. 3. Restart the application services. 4. Verify the fix is working.
🔧 Temporary Workarounds
Network Access Control
allRestrict network access to GCB Doctor systems using firewalls or network segmentation
Web Application Firewall
allDeploy WAF rules to block malicious file upload patterns
🧯 If You Can't Patch
- Isolate affected systems in a separate network segment with strict firewall rules
- Implement file upload restrictions at the web server level to block executable file types
🔍 How to Verify
Check if Vulnerable:
Attempt to upload a test file to the GCB Doctor file upload endpoint without authentication. If successful, the system is vulnerable.Check Version:
Check the GCB Doctor application version through the admin interface or configuration filesVerify Fix Applied:
After patching, attempt the same file upload test. It should fail with proper authentication or file type validation.📡 Detection & Monitoring
Log Indicators:
- Unusual file upload activity
- Multiple failed authentication attempts followed by successful uploads
- Execution of unexpected processes
Network Indicators:
- HTTP POST requests to file upload endpoints from unexpected sources
- Outbound connections from GCB Doctor systems to suspicious IPs
SIEM Query:
source="gcb_doctor_logs" AND (event="file_upload" AND user="anonymous") OR (process_execution="cmd.exe" OR process_execution="powershell.exe")