CVE-2021-1427
📋 TL;DR
This vulnerability in Cisco AnyConnect Secure Mobility Client for Windows allows authenticated local attackers to hijack DLL or executable files during install/uninstall/upgrade processes. Successful exploitation enables arbitrary code execution with SYSTEM privileges. Only affects Windows systems with vulnerable AnyConnect versions where attackers have valid local credentials.
💻 Affected Systems
- Cisco AnyConnect Secure Mobility Client
📦 What is this software?
⚠️ Risk & Real-World Impact
Worst Case
Attacker gains SYSTEM privileges on affected Windows systems, enabling complete system compromise, data theft, persistence, and lateral movement.
Likely Case
Privilege escalation from standard user to SYSTEM, allowing installation of malware, credential harvesting, or disabling security controls.
If Mitigated
Limited impact with proper patch management and least privilege principles, though local authenticated access still required.
🎯 Exploit Status
Requires local authenticated access and knowledge of DLL hijacking techniques during specific client operations.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: 4.10.00093 and later
Vendor Advisory: https://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-anyconnect-code-exec-jR3tWTA6
Restart Required: Yes
Instructions:
1. Download AnyConnect version 4.10.00093 or later from Cisco. 2. Uninstall current AnyConnect client. 3. Install updated version. 4. Restart system.
🔧 Temporary Workarounds
Restrict local user privileges
windowsImplement least privilege principles to limit users who can install/uninstall software
Monitor DLL loading
windowsUse Windows security tools to monitor and alert on suspicious DLL loading during AnyConnect operations
🧯 If You Can't Patch
- Implement strict access controls to limit local administrative privileges
- Monitor for suspicious DLL loading events and AnyConnect process manipulation
🔍 How to Verify
Check if Vulnerable:
Check AnyConnect version via GUI (Help > About) or registry: HKEY_LOCAL_MACHINE\SOFTWARE\Cisco\Cisco AnyConnect Secure Mobility Client\VersionCheck Version:
reg query "HKLM\SOFTWARE\Cisco\Cisco AnyConnect Secure Mobility Client" /v VersionVerify Fix Applied:
Confirm version is 4.10.00093 or higher using same methods📡 Detection & Monitoring
Log Indicators:
- Windows Event Logs showing DLL loading from unexpected locations during AnyConnect operations
- Process creation events for AnyConnect with unusual parent processes
Network Indicators:
- Unusual outbound connections from systems after AnyConnect install/uninstall operations
SIEM Query:
source="Windows Security" EventID=4688 ProcessName="*AnyConnect*" OR ProcessName="vpnui.exe" OR ProcessName="vpnagent.exe"