CVE-2020-37101: VPN Unlimited Privilege Escalation Flaw

CVE-2020-37101 Overview

CVE-2020-37101 is an unquoted service path vulnerability affecting VPN Unlimited version 6.1. This security flaw allows local attackers to inject malicious executables into the service binary path, potentially leading to privilege escalation on affected Windows systems. The vulnerability exists because the service executable path C:\Program Files (x86)\VPN Unlimited\ is not properly quoted, enabling attackers to place malicious binaries in strategic locations to be executed with elevated SYSTEM privileges.

Critical Impact

Local attackers can exploit this unquoted service path to replace the service executable and gain elevated system privileges, potentially compromising the entire system.

Affected Products

• VPN Unlimited 6.1 for Windows

Discovery Timeline

• 2026-02-03 - CVE CVE-2020-37101 published to NVD
• 2026-02-03 - Last updated in NVD database

Technical Details for CVE-2020-37101

Vulnerability Analysis

This vulnerability falls under CWE-428 (Unquoted Search Path or Element), a well-documented Windows security issue. When a Windows service is configured with an executable path containing spaces that is not enclosed in quotation marks, the Windows Service Control Manager (SCM) attempts to parse the path incorrectly. For the path C:\Program Files (x86)\VPN Unlimited\vpnservice.exe, Windows will attempt to execute in the following order:

1. C:\Program.exe
2. C:\Program Files.exe
3. C:\Program Files (x86)\VPN.exe
4. C:\Program Files (x86)\VPN Unlimited\vpnservice.exe

This behavior creates an opportunity for local attackers with write access to any of these directories to plant a malicious executable that will be executed with the privileges of the service—typically SYSTEM.

Root Cause

The root cause of this vulnerability is improper configuration during the software installation process. The VPN Unlimited installer registers the Windows service with an unquoted binary path in the Windows Registry. Proper installation practices require enclosing paths containing spaces within quotation marks to prevent path parsing ambiguity by the Windows Service Control Manager.

Attack Vector

The attack vector is local, requiring the attacker to have local access to the target system with sufficient write permissions to one of the parsed path locations. A typical exploitation scenario involves:

1. Attacker identifies the unquoted service path using tools like wmic service get name,displayname,pathname,startmode
2. Attacker crafts a malicious executable (e.g., reverse shell payload)
3. Attacker places the payload at a strategic location such as C:\Program Files (x86)\VPN.exe
4. When the VPN Unlimited service restarts or the system reboots, the malicious executable is executed with SYSTEM privileges

The exploitation does not require user interaction beyond waiting for a service restart or system reboot. Technical details and proof-of-concept information are available via the Exploit-DB #47916 advisory.

Detection Methods for CVE-2020-37101

Indicators of Compromise

• Unexpected executable files in C:\Program Files (x86)\ directory root (e.g., VPN.exe, Program.exe)
• Suspicious processes spawning from the VPN Unlimited service with unusual behavior
• Registry modifications to the VPN Unlimited service ImagePath value
• Unexpected network connections originating from processes in the VPN Unlimited installation directory

Detection Strategies

• Query Windows services for unquoted paths using WMI: wmic service get name,pathname | findstr /i "Program Files" | findstr /v """"
• Monitor file creation events in directories along the service path hierarchy
• Implement SentinelOne behavioral AI to detect anomalous process execution patterns from service contexts
• Enable Windows audit logging for service configuration changes and new process creation

Monitoring Recommendations

• Configure real-time file integrity monitoring on C:\Program Files (x86)\ and C:\Program Files\ root directories
• Monitor Windows Event Log for Service Control Manager events (Event ID 7045 for new service installation)
• Deploy SentinelOne endpoint protection with behavioral AI to detect privilege escalation attempts
• Regularly audit installed services for unquoted path vulnerabilities using automated scanning tools

How to Mitigate CVE-2020-37101

Immediate Actions Required

• Audit all installed Windows services for unquoted path vulnerabilities and remediate immediately
• Manually correct the registry entry by adding quotation marks around the service binary path
• Restrict write permissions on directories in the service path hierarchy to administrators only
• Monitor for unauthorized executable files in potentially affected directories

Patch Information

Users should check the VPN Unlimited Homepage for updated versions that address this vulnerability. Until a patch is available, manual remediation of the registry entry is recommended. Additional details can be found in the VulnCheck Advisory for VPN Unlimited.

Workarounds

• Manually quote the service path in the Windows Registry under HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\[ServiceName]\ImagePath
• Restrict file system permissions on C:\Program Files (x86)\ to prevent unauthorized file creation
• Implement application whitelisting to block unauthorized executables from running
• Use SentinelOne's endpoint protection to detect and block privilege escalation attempts in real-time

# Registry fix command (run as Administrator in CMD)
reg add "HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\VPNUnlimited" /v ImagePath /t REG_EXPAND_SZ /d "\"C:\Program Files (x86)\VPN Unlimited\vpnservice.exe\"" /f