CVE-2021-20051
📋 TL;DR
CVE-2021-20051 is a DLL search order hijacking vulnerability in SonicWall Global VPN Client installer versions 4.10.7.1117 and earlier. A local attacker can place a malicious DLL in a directory searched before legitimate system directories, leading to arbitrary command execution when the installer runs. This affects users running vulnerable versions of the SonicWall Global VPN Client installer.
💻 Affected Systems
- SonicWall Global VPN Client
📦 What is this software?
⚠️ Risk & Real-World Impact
Worst Case
Full system compromise with administrative privileges, allowing attacker persistence, data theft, and lateral movement.
Likely Case
Local privilege escalation leading to installation of malware, backdoors, or credential harvesting.
If Mitigated
Limited impact due to proper access controls preventing local attackers from placing files in vulnerable directories.
🎯 Exploit Status
Exploitation requires local access to place malicious DLL and trigger installer execution.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: 4.10.7.1118 or later
Vendor Advisory: https://psirt.global.sonicwall.com/vuln-detail/SNWLID-2021-0036
Restart Required: No
Instructions:
1. Download latest SonicWall Global VPN Client from official vendor site. 2. Uninstall previous version. 3. Install updated version. 4. Verify version is 4.10.7.1118 or newer.
🔧 Temporary Workarounds
Restrict installer directory permissions
windowsLimit write permissions to directories where installer runs to prevent DLL placement.
icacls "C:\Program Files\SonicWall\Global VPN Client" /deny Everyone:(OI)(CI)W
Use application whitelisting
windowsPrevent execution of unauthorized DLLs via application control policies.
🧯 If You Can't Patch
- Monitor for suspicious DLL files in installer directories
- Implement least privilege access controls to limit local user capabilities
🔍 How to Verify
Check if Vulnerable:
Check installed version via Control Panel > Programs and Features or registry: HKEY_LOCAL_MACHINE\SOFTWARE\SonicWall\Global VPN Client\VersionCheck Version:
reg query "HKLM\SOFTWARE\SonicWall\Global VPN Client" /v VersionVerify Fix Applied:
Confirm version is 4.10.7.1118 or newer using same methods.📡 Detection & Monitoring
Log Indicators:
- Windows Event Logs showing DLL loading from unexpected locations
- Process creation events for installer with suspicious parent processes
Network Indicators:
- Unusual outbound connections following installer execution
SIEM Query:
EventID=4688 AND (ProcessName="*SonicWall*" OR CommandLine="*SonicWall*") AND ParentProcessName="explorer.exe"