CVE-2021-34788
📋 TL;DR
This vulnerability allows authenticated local attackers to execute arbitrary code with root privileges on Linux and Mac OS systems running Cisco AnyConnect with the VPN Posture (HostScan) Module. Attackers exploit a race condition in shared library signature verification by sending crafted IPC messages. Only systems with the HostScan module installed are affected.
💻 Affected Systems
- Cisco AnyConnect Secure Mobility Client
📦 What is this software?
⚠️ Risk & Real-World Impact
Worst Case
Full system compromise with root privileges, allowing complete control over the affected device, data theft, and lateral movement within the network.
Likely Case
Local privilege escalation leading to persistence, credential harvesting, and installation of backdoors on individual workstations.
If Mitigated
Limited impact due to proper access controls, monitoring, and timely patching preventing successful exploitation.
🎯 Exploit Status
Requires local authenticated access and knowledge of race condition exploitation techniques. The HostScan module must be present.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: 4.10.02093 and later
Vendor Advisory: https://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-anyconnect-lib-hija-cAFB7x4q
Restart Required: Yes
Instructions:
1. Download AnyConnect version 4.10.02093 or later from Cisco's website. 2. Uninstall the current AnyConnect client. 3. Install the updated version. 4. Restart the system to ensure all components are loaded correctly.
🔧 Temporary Workarounds
Remove HostScan Module
linuxUninstall the VPN Posture (HostScan) Module if not required for compliance or security policies.
sudo /opt/cisco/anyconnect/bin/vpn_uninstall.sh posture
Restrict Local Access
allImplement strict access controls to limit local user accounts and monitor for suspicious IPC activity.
🧯 If You Can't Patch
- Remove the HostScan module if posture assessment is not required
- Implement strict local account controls and monitor for unusual IPC communications
🔍 How to Verify
Check if Vulnerable:
Check AnyConnect version with 'anyconnect -v' and verify if HostScan module is installed in /opt/cisco/anyconnect/bin/Check Version:
anyconnect -vVerify Fix Applied:
Confirm version is 4.10.02093 or higher and check that HostScan module files have been updated or removed📡 Detection & Monitoring
Log Indicators:
- Unusual IPC message patterns to AnyConnect process
- Failed signature verification attempts in system logs
- Unexpected shared library loading events
Network Indicators:
- Local IPC traffic spikes to AnyConnect process
SIEM Query:
process_name:"anyconnect" AND event_type:"library_load" AND result:"failed"