CVE-2020-27172
📋 TL;DR
This vulnerability in G-Data antivirus software allows attackers to use symbolic links to abuse the infected-file restore mechanism, leading to arbitrary file writes and privilege escalation. It affects G-Data antivirus users with versions before 25.5.9.25. Attackers with local access can exploit this to gain elevated privileges on the system.
💻 Affected Systems
- G-Data Antivirus
📦 What is this software?
G Data by Gdatasoftware
⚠️ Risk & Real-World Impact
Worst Case
Full system compromise with administrative privileges, allowing complete control over the affected system, data theft, and lateral movement within the network.
Likely Case
Local privilege escalation where an authenticated user gains administrative privileges, potentially leading to persistence mechanisms, credential harvesting, or disabling security controls.
If Mitigated
Limited impact if proper access controls restrict local user privileges and antivirus software is kept updated.
🎯 Exploit Status
Exploitation requires local access and knowledge of symbolic link abuse techniques. The vulnerability is well-documented in security advisories.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: 25.5.9.25 and later
Vendor Advisory: https://www.gdatasoftware.com/security-advisory
Restart Required: Yes
Instructions:
1. Open G-Data antivirus software. 2. Navigate to Update section. 3. Check for and install updates. 4. Restart the system to complete the update process.
🔧 Temporary Workarounds
Disable infected-file restore feature
windowsTemporarily disable the infected-file restore mechanism to prevent exploitation while awaiting patch deployment.
Open G-Data settings > Protection > Quarantine > Disable 'Restore infected files' option
Restrict symbolic link creation
windowsConfigure Windows security policy to restrict symbolic link creation to administrators only.
gpedit.msc > Computer Configuration > Windows Settings > Security Settings > Local Policies > User Rights Assignment > 'Create symbolic links' > Remove all users except Administrators
🧯 If You Can't Patch
- Implement strict access controls to limit local user privileges and prevent unauthorized users from accessing systems.
- Monitor for suspicious file operations and privilege escalation attempts using endpoint detection and response (EDR) tools.
🔍 How to Verify
Check if Vulnerable:
Check G-Data antivirus version in the software interface or via 'gdata' command if available. Versions below 25.5.9.25 are vulnerable.Check Version:
Check G-Data software interface under 'About' or 'Help' > 'About' section for version information.Verify Fix Applied:
Verify the installed version is 25.5.9.25 or higher in G-Data antivirus settings.📡 Detection & Monitoring
Log Indicators:
- Unusual file restore operations in G-Data logs
- Multiple failed restore attempts
- Symbolic link creation events in Windows security logs
Network Indicators:
- Local privilege escalation attempts typically don't generate network traffic
SIEM Query:
EventID=4688 AND ProcessName LIKE '%gdata%' AND CommandLine CONTAINS 'restore' OR EventID=4656 AND ObjectName LIKE '%symlink%'