CVE-2024-20501
📋 TL;DR
This vulnerability allows unauthenticated remote attackers to cause denial of service on Cisco Meraki MX and Z Series devices by sending crafted HTTPS requests to the AnyConnect VPN server. Attackers can force VPN service restarts, disconnect active users, and potentially prevent new connections. Organizations using affected Cisco Meraki VPN gateways are at risk.
💻 Affected Systems
- Cisco Meraki MX Series
- Cisco Meraki Z Series Teleworker Gateway
📦 What is this software?
⚠️ Risk & Real-World Impact
Worst Case
Sustained attacks could completely prevent VPN connectivity, disrupting remote workforce access to internal resources and potentially affecting business operations.
Likely Case
Intermittent VPN service disruptions causing remote users to lose connections and need to reconnect, creating productivity impact and user frustration.
If Mitigated
Brief service interruptions during attack periods with automatic recovery, minimal business impact due to quick reconnection capability.
🎯 Exploit Status
Exploitation requires sending crafted HTTPS requests to VPN server; no authentication needed
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Check Cisco advisory for specific firmware versions
Vendor Advisory: https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-meraki-mx-vpn-dos-QTRHzG2
Restart Required: Yes
Instructions:
1. Log into Meraki dashboard 2. Navigate to Security & SD-WAN > Configure > Firewall 3. Check firmware version 4. Update to latest firmware 5. Reboot device after update
🔧 Temporary Workarounds
Restrict VPN Access
allLimit VPN server access to trusted IP ranges using firewall rules
Disable AnyConnect Temporarily
allTemporarily disable AnyConnect VPN if not critically needed
🧯 If You Can't Patch
- Implement network segmentation to isolate VPN servers
- Deploy intrusion prevention systems to detect and block attack patterns
🔍 How to Verify
Check if Vulnerable:
Check Meraki dashboard for firmware version and compare against patched versions in Cisco advisoryCheck Version:
Check via Meraki dashboard: Security & SD-WAN > Configure > FirewallVerify Fix Applied:
Verify firmware version is updated to patched version and monitor VPN service stability📡 Detection & Monitoring
Log Indicators:
- Multiple VPN service restarts
- Unusual HTTPS request patterns to VPN endpoint
- Spike in failed connection attempts
Network Indicators:
- Unusual traffic volume to VPN port 443
- Multiple connection resets from same source IPs
SIEM Query:
source="meraki" AND ("VPN restart" OR "AnyConnect service" AND failure)