CVE-2021-21964
📋 TL;DR
A denial of service vulnerability in Sealevel Systems SeaConnect 370W's Modbus configuration allows attackers to crash the device by sending specially-crafted network packets. This affects organizations using SeaConnect 370W v1.3.34 for industrial control systems. The vulnerability requires network access to the device's Modbus interface.
💻 Affected Systems
- Sealevel Systems SeaConnect 370W
📦 What is this software?
⚠️ Risk & Real-World Impact
Worst Case
Complete device unavailability requiring physical reset or power cycle, disrupting industrial processes and potentially causing safety or production impacts.
Likely Case
Temporary service disruption requiring manual intervention to restore functionality, causing operational downtime.
If Mitigated
No impact if device is properly segmented and protected from untrusted networks.
🎯 Exploit Status
Exploitation requires sending crafted packets to Modbus port; no authentication needed.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: v1.3.35 or later
Vendor Advisory: https://www.sealevel.com/support/security-advisories/
Restart Required: Yes
Instructions:
1. Download latest firmware from Sealevel support portal. 2. Backup current configuration. 3. Upload new firmware via web interface. 4. Restart device. 5. Restore configuration if needed.
🔧 Temporary Workarounds
Network Segmentation
allIsolate SeaConnect devices from untrusted networks using firewalls or VLANs.
Access Control Lists
linuxRestrict Modbus port access to authorized IP addresses only.
iptables -A INPUT -p tcp --dport 502 -s trusted_ip -j ACCEPT
iptables -A INPUT -p tcp --dport 502 -j DROP
🧯 If You Can't Patch
- Implement strict network segmentation to isolate SeaConnect devices
- Deploy intrusion detection systems to monitor for malicious Modbus traffic
🔍 How to Verify
Check if Vulnerable:
Check device firmware version via web interface or serial console; if version is v1.3.34, device is vulnerable.Check Version:
Check via web interface at http://device-ip/status or serial console command 'version'Verify Fix Applied:
Confirm firmware version is v1.3.35 or later and test Modbus functionality remains operational.📡 Detection & Monitoring
Log Indicators:
- Device crash/restart logs
- Modbus connection errors
- Unusual packet patterns on port 502
Network Indicators:
- Malformed Modbus packets to port 502
- Sudden traffic spikes to device
- Connection attempts from unauthorized sources
SIEM Query:
source_port:502 AND (packet_size:unusual OR protocol_violation:true)