CVE-2025-20271
📋 TL;DR
An unauthenticated remote attacker can cause denial of service on Cisco Meraki MX and Z Series devices by sending crafted HTTPS requests to the AnyConnect VPN server. This vulnerability allows attackers to restart the VPN service, disrupting all active VPN connections and potentially preventing new connections. Organizations using affected Cisco Meraki devices with AnyConnect VPN enabled are vulnerable.
💻 Affected Systems
- Cisco Meraki MX Series
- Cisco Meraki Z Series Teleworker Gateway
⚠️ Manual Verification Required
This CVE does not have specific version information in our database, so automatic vulnerability detection cannot determine if your system is affected.
Why? The CVE database entry doesn't specify which versions are vulnerable (no version ranges provided by the vendor/NVD).
🔒 Custom verification scripts are available for registered users. Sign up free to download automated test scripts.
- Review the CVE details at NVD
- Check vendor security advisories for your specific version
- Test if the vulnerability is exploitable in your environment
- Consider updating to the latest version as a precaution
⚠️ Risk & Real-World Impact
Worst Case
Sustained attacks could completely disable VPN connectivity for all remote users, disrupting business operations and remote workforce access.
Likely Case
Intermittent VPN service disruptions causing connection drops and requiring users to reconnect, creating productivity impact.
If Mitigated
Minimal impact with proper network segmentation and monitoring allowing quick detection and response to attack attempts.
🎯 Exploit Status
Exploitation requires sending crafted HTTPS requests to the VPN service, which is relatively straightforward for attackers with network access.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Check Cisco Security Advisory for specific patched versions
Vendor Advisory: https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-meraki-mx-vpn-dos-sM5GCfm7
Restart Required: Yes
Instructions:
1. Log into Cisco Meraki dashboard. 2. Navigate to Security & SD-WAN > Configure > Site-to-site VPN. 3. Apply the latest firmware update for affected devices. 4. Reboot devices after update completion.
🔧 Temporary Workarounds
Restrict VPN Access
allLimit VPN access to trusted IP addresses using firewall rules to reduce attack surface.
Disable AnyConnect Temporarily
allTemporarily disable Cisco AnyConnect VPN service if not critically needed while awaiting patch.
🧯 If You Can't Patch
- Implement network segmentation to isolate VPN traffic and limit blast radius
- Deploy rate limiting and DDoS protection for VPN endpoints
🔍 How to Verify
Check if Vulnerable:
Check device firmware version in Cisco Meraki dashboard and compare against patched versions in advisory.Check Version:
Check version in Meraki dashboard under Organization > Inventory or device status pageVerify Fix Applied:
Verify firmware version has been 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 VPN connection attempts
Network Indicators:
- Unusual traffic patterns to VPN port (typically 443)
- Multiple connection resets from single sources
SIEM Query:
source="meraki" AND ("VPN restart" OR "AnyConnect service" AND "failed")