CVE-2021-1496
📋 TL;DR
This vulnerability allows authenticated local attackers on Windows systems with Cisco AnyConnect Secure Mobility Client to hijack DLL or executable files during installation/uninstallation/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
📦 What is this software?
⚠️ Risk & Real-World Impact
Worst Case
Attacker gains SYSTEM privileges and full control of the Windows system, enabling persistent access, data theft, lateral movement, and complete compromise.
Likely Case
Privilege escalation from standard user to SYSTEM, allowing installation of malware, credential harvesting, and persistence mechanisms.
If Mitigated
Limited impact with proper access controls, least privilege principles, and timely patching preventing exploitation.
🎯 Exploit Status
Requires local authenticated access and knowledge of specific file placement during installation/uninstallation processes.
🛠️ 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 installation directory permissions
windowsSet strict permissions on AnyConnect installation directories to prevent unauthorized file placement
icacls "C:\Program Files (x86)\Cisco\Cisco AnyConnect Secure Mobility Client" /inheritance:r /grant:r "SYSTEM:(OI)(CI)F" "Administrators:(OI)(CI)F" /deny "Users:(OI)(CI)(W)"
🧯 If You Can't Patch
- Implement strict access controls to limit who has local login access to systems with AnyConnect
- Monitor for unauthorized file creation in AnyConnect directories and installation/uninstallation events
🔍 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 unauthorized file creation in Cisco directories
- AnyConnect installation/uninstallation events from unexpected users
Network Indicators:
- Unusual outbound connections from systems after AnyConnect maintenance
SIEM Query:
EventID=4688 AND (ProcessName LIKE '%anyconnect%' OR CommandLine LIKE '%anyconnect%') AND SubjectUserName NOT IN (expected_admin_users)