CVE-2021-20046
📋 TL;DR
A stack-based buffer overflow vulnerability in SonicOS firewalls allows remote authenticated attackers to cause denial of service and potentially execute arbitrary code by sending specially crafted HTTP Content-Length response headers. This affects SonicWall firewalls running Gen 5, Gen 6, and Gen 7 firmware versions. Attackers need authentication to exploit this vulnerability.
💻 Affected Systems
- SonicWall firewalls with SonicOS
📦 What is this software?
Sonicos by Sonicwall
Sonicos by Sonicwall
Sonicos by Sonicwall
Sonicos by Sonicwall
Sonicos by Sonicwall
Sonicos by Sonicwall
Sonicos by Sonicwall
⚠️ Risk & Real-World Impact
Worst Case
Remote code execution leading to complete firewall compromise, lateral movement into protected networks, and persistent backdoor installation.
Likely Case
Denial of service causing firewall crash and network disruption, requiring manual reboot to restore functionality.
If Mitigated
Limited to authenticated users only, reducing attack surface to authorized personnel or compromised credentials.
🎯 Exploit Status
Exploitation requires authentication, which reduces immediate risk but increases danger if credentials are compromised.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Check SonicWall security advisory for specific patched versions
Vendor Advisory: https://psirt.global.sonicwall.com/vuln-detail/SNWLID-2021-0027
Restart Required: Yes
Instructions:
1. Log into SonicWall management interface. 2. Navigate to System > Firmware. 3. Download and install the latest firmware version. 4. Reboot the firewall after installation completes.
🔧 Temporary Workarounds
Restrict Management Access
allLimit firewall management interface access to trusted IP addresses only
Implement Strong Authentication
allEnforce multi-factor authentication and strong password policies for firewall administration
🧯 If You Can't Patch
- Implement network segmentation to isolate firewall management interfaces
- Monitor for unusual authentication attempts and firewall crashes
🔍 How to Verify
Check if Vulnerable:
Check firmware version in SonicWall management interface under System > StatusCheck Version:
Show version (via CLI) or check System > Status (via GUI)Verify Fix Applied:
Verify firmware version matches patched version from SonicWall advisory📡 Detection & Monitoring
Log Indicators:
- Firewall crash logs
- Multiple failed authentication attempts followed by successful login
- Unusual HTTP traffic patterns to management interface
Network Indicators:
- Unexpected firewall reboots
- Management interface receiving malformed HTTP headers
SIEM Query:
source="sonicwall" AND (event_type="crash" OR (http_content_length>10000 AND auth_success="true"))