CVE-2020-5135
📋 TL;DR
CVE-2020-5135 is a critical buffer overflow vulnerability in SonicOS firewalls that allows remote attackers to cause denial of service or potentially execute arbitrary code by sending malicious requests. This affects SonicWall firewall appliances running vulnerable versions of SonicOS Gen 6 and Gen 7. Organizations using affected SonicWall firewalls are at risk of complete system compromise.
💻 Affected Systems
- SonicWall firewalls with SonicOS
📦 What is this software?
Sonicos by Sonicwall
Sonicos by Sonicwall
Sonicos by Sonicwall
Sonicos by Sonicwall
Sonicosv by Sonicwall
⚠️ Risk & Real-World Impact
Worst Case
Remote code execution leading to full firewall compromise, network infiltration, and persistent backdoor installation
Likely Case
Denial of service causing firewall outage and network disruption
If Mitigated
Limited impact if firewalls are patched, properly segmented, and have intrusion prevention enabled
🎯 Exploit Status
This vulnerability is listed in CISA's Known Exploited Vulnerabilities catalog, confirming active exploitation in the wild. Attackers can exploit without authentication.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: SonicOS Gen 6: 6.5.4.7-83n, 6.5.1.12-1n, 6.0.5.3-93o; SonicOS Gen 7: 7.0.0.0-1
Vendor Advisory: https://psirt.global.sonicwall.com/vuln-detail/SNWLID-2020-0010
Restart Required: Yes
Instructions:
1. Log into SonicWall firewall management interface. 2. Navigate to System > Settings > Firmware & Backups. 3. Download appropriate patched firmware from MySonicWall portal. 4. Upload and install firmware update. 5. Reboot firewall after installation completes.
🔧 Temporary Workarounds
Network Segmentation
allRestrict access to SonicWall management interfaces to trusted networks only
Configure firewall rules to limit management interface access to specific IP ranges
Intrusion Prevention
allEnable SonicWall IPS signatures for CVE-2020-5135 detection and prevention
Enable IPS signature ID 10555 in SonicWall IPS settings
🧯 If You Can't Patch
- Isolate affected firewalls from internet access using upstream firewalls or ACLs
- Implement strict network segmentation to limit blast radius if compromised
🔍 How to Verify
Check if Vulnerable:
Check SonicOS version in System > Status > System Status page in management interfaceCheck Version:
From CLI: show version | grep SonicOSVerify Fix Applied:
Verify SonicOS version matches patched versions listed in vendor advisory📡 Detection & Monitoring
Log Indicators:
- Multiple connection attempts to firewall management interface from unusual sources
- Firewall crash/restart logs
- IPS alerts for signature 10555
Network Indicators:
- Unusual traffic patterns to firewall management ports (default 443, 80)
- Malformed HTTP/HTTPS requests to firewall
SIEM Query:
source="sonicwall" AND (event_type="crash" OR event_type="restart") OR signature_id="10555"