CVE-2020-5137
📋 TL;DR
A buffer overflow vulnerability in SonicOS SSLVPN service allows remote unauthenticated attackers to crash the firewall via denial of service. This affects multiple SonicWall firewall generations and versions, potentially disrupting VPN connectivity and firewall operations.
💻 Affected Systems
- SonicWall SonicOS
📦 What is this software?
Sonicos by Sonicwall
Sonicos by Sonicwall
Sonicos by Sonicwall
Sonicos by Sonicwall
Sonicos by Sonicwall
Sonicosv by Sonicwall
⚠️ Risk & Real-World Impact
Worst Case
Complete firewall crash requiring physical reboot, extended VPN service outage, and potential loss of network connectivity for protected systems.
Likely Case
SSLVPN service disruption causing VPN connectivity loss for remote users, requiring firewall reboot to restore service.
If Mitigated
Minimal impact if firewall automatically restarts services, but temporary VPN connectivity interruption still occurs.
🎯 Exploit Status
Buffer overflow vulnerabilities in network services often have public exploits developed. The unauthenticated nature makes this particularly dangerous.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Check SonicWall advisory for specific fixed versions per generation
Vendor Advisory: https://psirt.global.sonicwall.com/vuln-detail/SNWLID-2020-0012
Restart Required: Yes
Instructions:
1. Log into SonicWall management interface. 2. Navigate to System > Settings > Firmware & Backups. 3. Download appropriate firmware update from SonicWall support portal. 4. Upload and install firmware. 5. Reboot firewall after installation completes.
🔧 Temporary Workarounds
Disable SSLVPN Service
allTemporarily disable the vulnerable SSLVPN service to prevent exploitation
Navigate to VPN > SSL-VPN > Server Settings and disable 'Enable SSL-VPN'
Restrict SSLVPN Access
allLimit SSLVPN access to specific IP ranges using firewall rules
Create access rule limiting WAN to SSLVPN service to trusted IP addresses only
🧯 If You Can't Patch
- Implement network segmentation to isolate firewall management interfaces
- Deploy intrusion prevention system (IPS) with signatures for SonicWall buffer overflow attacks
🔍 How to Verify
Check if Vulnerable:
Check System > Status > Firmware Version in SonicWall management interface and compare with affected versions listCheck Version:
From CLI: show version | include SonicOSVerify Fix Applied:
Verify firmware version has been updated to a version not listed in affected versions, then test SSLVPN connectivity📡 Detection & Monitoring
Log Indicators:
- Firewall crash/reboot events
- SSLVPN service restart failures
- High volume of malformed packets to SSLVPN port (typically 4433)
Network Indicators:
- Unusual traffic patterns to SSLVPN port
- Firewall becoming unresponsive
- VPN connectivity disruptions
SIEM Query:
source="sonicwall" AND (event_type="crash" OR event_type="reboot" OR service="sslvpn" AND status="failed")