CVE-2021-1429
📋 TL;DR
This vulnerability allows authenticated local attackers on Windows systems with Cisco AnyConnect Secure Mobility Client to hijack DLL or executable files during install/uninstall/upgrade processes. Successful exploitation enables arbitrary code execution with SYSTEM privileges. Only affects users with valid Windows credentials on systems running vulnerable AnyConnect versions.
💻 Affected Systems
- Cisco AnyConnect Secure Mobility Client for Windows
📦 What is this software?
⚠️ Risk & Real-World Impact
Worst Case
Attacker gains SYSTEM privileges and full control of the Windows system, enabling data theft, persistence, lateral movement, and complete compromise.
Likely Case
Privilege escalation from standard user to SYSTEM, allowing installation of malware, credential harvesting, and bypassing security controls.
If Mitigated
Limited impact with proper patch management and least privilege principles; attacker would need valid credentials and local access.
🎯 Exploit Status
Exploitation requires local authenticated access and knowledge of vulnerable DLL/executable paths during install/uninstall/upgrade 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 principle to limit which users can install/uninstall software
Monitor DLL hijacking attempts
windowsEnable auditing for DLL loading from untrusted locations
auditpol /set /subcategory:"Detailed File Share" /success:enable /failure:enable
🧯 If You Can't Patch
- Implement strict access controls to limit which users have local login privileges
- Monitor for suspicious DLL loading behavior and AnyConnect install/uninstall activities
🔍 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 unusual paths
- AnyConnect install/uninstall events from unexpected users
Network Indicators:
- Unusual outbound connections after AnyConnect operations
SIEM Query:
EventID=4688 AND (ProcessName LIKE '%anyconnect%' OR CommandLine LIKE '%anyconnect%') AND SubjectUserName NOT IN (allowed_users)