CVE-2020-3556
📋 TL;DR
A local privilege escalation vulnerability in Cisco AnyConnect Secure Mobility Client allows authenticated local attackers to execute arbitrary scripts with the privileges of a targeted AnyConnect user. The vulnerability exists in the interprocess communication (IPC) channel due to lack of authentication. Affected users are those running vulnerable AnyConnect versions with active VPN sessions.
💻 Affected Systems
- Cisco AnyConnect Secure Mobility Client
📦 What is this software?
Anyconnect Secure Mobility Client by Cisco
⚠️ Risk & Real-World Impact
Worst Case
An attacker with local system access could execute arbitrary code with the privileges of any logged-in AnyConnect user, potentially leading to full system compromise, data theft, or lateral movement within the network.
Likely Case
A malicious insider or compromised account could execute scripts to steal credentials, install malware, or perform reconnaissance on the local system and connected networks.
If Mitigated
With proper access controls and monitoring, impact would be limited to the specific user's privileges, potentially allowing file access or local system changes but preventing network-wide compromise.
🎯 Exploit Status
Exploitation requires local system access, valid user credentials, and knowledge of IPC communication. The attacker must craft specific IPC messages to trigger script execution.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Not released
Vendor Advisory: https://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-anyconnect-ipc-KfQO9QhK
Restart Required: No
Instructions:
No official patch available. Monitor Cisco Security Advisory for updates and apply immediately when released.
🔧 Temporary Workarounds
Restrict Local Access
allLimit local system access to trusted users only and implement strict access controls to reduce attack surface.
Monitor IPC Activity
allImplement monitoring for unusual IPC channel activity or script execution from AnyConnect processes.
🧯 If You Can't Patch
- Implement strict principle of least privilege for all user accounts
- Deploy endpoint detection and response (EDR) solutions to monitor for suspicious script execution
🔍 How to Verify
Check if Vulnerable:
Check AnyConnect version and compare against Cisco Security Advisory. Vulnerable if running any version prior to the fix (when released).Check Version:
Windows: 'anyconnect.exe --version' or check installed programs. Linux/macOS: Check package version or run AnyConnect with --version flag.Verify Fix Applied:
Once patch is available, verify AnyConnect version matches or exceeds the patched version specified in Cisco advisory.📡 Detection & Monitoring
Log Indicators:
- Unusual IPC communication to AnyConnect processes
- Script execution originating from AnyConnect user sessions
- Failed authentication attempts to IPC channels
Network Indicators:
- Localhost IPC traffic patterns matching exploit signatures
- Unexpected outbound connections from AnyConnect processes
SIEM Query:
Process creation where parent process contains 'anyconnect' AND (command line contains 'powershell' OR 'cmd' OR 'bash' OR 'python')