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Designs IEC 62443-3-2 security zones/conduits for IACS/OT networks via risk partitioning, SL-T targets, firewall microsegmentation, and Purdue model validation.
npx claudepluginhub mukul975/anthropic-cybersecurity-skills --plugin cybersecurity-skillsThis skill uses the workspace's default tool permissions.
- When designing a greenfield OT network architecture for a new industrial facility
Applies Acme Corporation brand guidelines including colors, fonts, layouts, and messaging to generated PowerPoint, Excel, and PDF documents.
Builds DCF models with sensitivity analysis, Monte Carlo simulations, and scenario planning for investment valuation and risk assessment.
Calculates profitability (ROE, margins), liquidity (current ratio), leverage, efficiency, and valuation (P/E, EV/EBITDA) ratios from financial statements in CSV, JSON, text, or Excel for investment analysis.
Do not use for IT-only network segmentation (see implementing-network-microsegmentation), for cloud-native workload segmentation (see securing-kubernetes-on-cloud), or for physical security zone design without a cyber component.
Partition the IACS into zones based on functional requirements, security requirements, criticality, and consequence of compromise. Each zone contains assets with common security requirements.
# IEC 62443-3-2 Zone Definition Document
facility: "Petrochemical Refinery - Unit 3"
assessment_date: "2026-02-23"
standard: "IEC 62443-3-2:2020"
zones:
- zone_id: "Z1-SIS"
name: "Safety Instrumented Systems"
purdue_level: 1
security_level_target: "SL 3"
criticality: "Safety Critical"
assets:
- "Triconex 3008 Safety Controller (SIS-01)"
- "Triconex 3008 Safety Controller (SIS-02)"
- "SIS Engineering Workstation"
security_requirements:
- "Physically isolated from all other zones (air-gapped)"
- "Dedicated engineering workstation with removable media controls"
- "No remote access permitted under any circumstances"
- "Change management requires dual authorization"
allowed_conduits: [] # No network conduits - fully air-gapped
- zone_id: "Z2-BPCS"
name: "Basic Process Control System"
purdue_level: "1-2"
security_level_target: "SL 2"
criticality: "High"
assets:
- "Allen-Bradley ControlLogix PLCs (PLC-01 through PLC-12)"
- "Rockwell FactoryTalk View HMIs (HMI-01 through HMI-06)"
- "Engineering Workstation (EWS-01)"
security_requirements:
- "Industrial firewall at zone boundary with protocol inspection"
- "Read-only access from Level 3 for data acquisition"
- "Write access restricted to engineering workstation subnet"
- "USB ports disabled on HMIs"
allowed_conduits: ["C1-BPCS-OPS"]
- zone_id: "Z3-OPS"
name: "Site Operations"
purdue_level: 3
security_level_target: "SL 2"
criticality: "Medium"
assets:
- "OSIsoft PI Historian (HIST-01)"
- "OPC UA Server (OPC-01)"
- "MES Application Server (MES-01)"
- "Alarm Management Server (ALM-01)"
security_requirements:
- "Firewall between operations and control zones"
- "Firewall between operations and DMZ"
- "No direct internet access"
- "Antivirus with OT-approved signatures"
allowed_conduits: ["C1-BPCS-OPS", "C2-OPS-DMZ"]
- zone_id: "Z4-DMZ"
name: "Industrial Demilitarized Zone"
purdue_level: 3.5
security_level_target: "SL 2"
criticality: "Medium"
assets:
- "PI-to-PI Interface (DMZ-HIST-01)"
- "Patch Management Server (DMZ-WSUS-01)"
- "Remote Access Jump Server (DMZ-JUMP-01)"
- "Data Diode - Waterfall Security (DMZ-DD-01)"
security_requirements:
- "Dual-homed firewalls on both sides"
- "No direct traffic traversal - all connections terminate in DMZ"
- "Data diode for unidirectional historian replication"
- "Jump server with MFA for remote access"
allowed_conduits: ["C2-OPS-DMZ", "C3-DMZ-ENT"]
- zone_id: "Z5-ENT"
name: "Enterprise Network"
purdue_level: 4
security_level_target: "SL 1"
criticality: "Low (from OT perspective)"
assets:
- "Corporate systems accessing OT data"
security_requirements:
- "Firewall between enterprise and DMZ"
- "No direct access to any OT zone below DMZ"
allowed_conduits: ["C3-DMZ-ENT"]
conduits:
- conduit_id: "C1-BPCS-OPS"
name: "Control-to-Operations Conduit"
connects: ["Z2-BPCS", "Z3-OPS"]
security_level: "SL 2"
protocols_allowed:
- protocol: "OPC UA"
port: 4840
direction: "Z2 -> Z3 (read only)"
security_mode: "SignAndEncrypt"
- protocol: "Modbus/TCP"
port: 502
direction: "Z3 -> Z2 (read only, FC 3/4 only)"
security_mode: "Firewall-enforced function code filtering"
controls:
- "Industrial firewall with OT protocol DPI"
- "Allowlisted source/destination IP pairs"
- "Function code filtering (block all write operations from L3)"
- "Connection rate limiting"
- conduit_id: "C2-OPS-DMZ"
name: "Operations-to-DMZ Conduit"
connects: ["Z3-OPS", "Z4-DMZ"]
security_level: "SL 2"
protocols_allowed:
- protocol: "PI-to-PI"
port: 5450
direction: "Z3 -> Z4 (unidirectional via data diode)"
- protocol: "HTTPS"
port: 443
direction: "Z4 -> Z3 (patch downloads only)"
controls:
- "Data diode for historian replication (Waterfall Security)"
- "Firewall with application-layer inspection"
- "Patch server pulls only from approved vendor repositories"
- conduit_id: "C3-DMZ-ENT"
name: "DMZ-to-Enterprise Conduit"
connects: ["Z4-DMZ", "Z5-ENT"]
security_level: "SL 1"
protocols_allowed:
- protocol: "HTTPS"
port: 443
direction: "Z5 -> Z4 (historian read, remote access portal)"
- protocol: "RDP"
port: 3389
direction: "Z5 -> Z4 (jump server with MFA)"
controls:
- "Next-gen firewall with SSL inspection"
- "MFA required for all remote access sessions"
- "Session recording on jump server"
Deploy and configure industrial-grade firewalls at each zone boundary with OT protocol-aware deep packet inspection.
# Cisco ISA-3000 Industrial Firewall Configuration
# Conduit C1: BPCS (Zone 2) <-> Operations (Zone 3)
# Define zone interfaces
interface GigabitEthernet1/1
nameif zone-bpcs
security-level 90
ip address 10.20.1.1 255.255.0.0
interface GigabitEthernet1/2
nameif zone-ops
security-level 70
ip address 10.30.1.1 255.255.0.0
# OPC UA from BPCS to Operations (read-only data flow)
access-list BPCS-to-OPS extended permit tcp 10.20.0.0 255.255.0.0 host 10.30.1.50 eq 4840
# Modbus read from Operations historian to PLCs (FC 3,4 only)
access-list OPS-to-BPCS extended permit tcp host 10.30.1.50 10.20.0.0 255.255.0.0 eq 502
# Deny all other traffic between zones
access-list BPCS-to-OPS extended deny ip any any log
access-list OPS-to-BPCS extended deny ip any any log
# Apply access lists
access-group BPCS-to-OPS in interface zone-bpcs
access-group OPS-to-BPCS in interface zone-ops
# Enable Modbus protocol inspection with function code filtering
policy-map type inspect modbus MODBUS-INSPECT
parameters
# Allow read operations only from Operations zone
match func-code read-coils
match func-code read-discrete-inputs
match func-code read-holding-registers
match func-code read-input-registers
# Block all write function codes
match func-code force-single-coil action drop log
match func-code preset-single-register action drop log
match func-code force-multiple-coils action drop log
match func-code preset-multiple-registers action drop log
# Apply to service policy
policy-map global_policy
class inspection_default
inspect modbus MODBUS-INSPECT
# Logging to OT SIEM
logging host zone-ops 10.30.1.60
logging trap informational
logging enable
Configure network switches to enforce zone boundaries at Layer 2, preventing broadcast domain overlap between Purdue levels.
# Cisco Industrial Ethernet Switch Configuration
# Zone-based VLAN assignment
# VLAN definitions aligned with zones
vlan 10
name Z1-SIS-Safety
vlan 20
name Z2-BPCS-Control
vlan 30
name Z3-OPS-Operations
vlan 35
name Z4-DMZ
vlan 40
name Z5-Enterprise
# PLC ports - Zone 2 BPCS
interface range GigabitEthernet1/0/1-12
description PLC connections - Zone 2
switchport mode access
switchport access vlan 20
switchport port-security
switchport port-security maximum 1
switchport port-security mac-address sticky
switchport port-security violation shutdown
spanning-tree portfast
spanning-tree bpduguard enable
no cdp enable
no lldp transmit
# HMI ports - Zone 2 BPCS
interface range GigabitEthernet1/0/13-18
description HMI connections - Zone 2
switchport mode access
switchport access vlan 20
switchport port-security
switchport port-security maximum 1
switchport port-security mac-address sticky
switchport port-security violation restrict
spanning-tree portfast
# Trunk to industrial firewall
interface GigabitEthernet1/0/24
description Trunk to ISA-3000 Firewall
switchport mode trunk
switchport trunk allowed vlan 20,30,35
switchport trunk native vlan 999
# Disable unused ports
interface range GigabitEthernet1/0/19-23
shutdown
switchport access vlan 999
Install a hardware-enforced data diode between the operations zone and DMZ to ensure unidirectional data flow from OT to IT. Data diodes physically prevent any data from flowing back into the OT network.
#!/usr/bin/env python3
"""Data Diode Configuration Validator.
Validates that historian replication across the data diode
(Waterfall Security, Owl Cyber Defense, or Siemens) is
functioning correctly with unidirectional enforcement.
"""
import socket
import struct
import time
import json
from datetime import datetime
class DataDiodeValidator:
"""Validates data diode unidirectional enforcement."""
def __init__(self, diode_tx_ip, diode_rx_ip, historian_port=5450):
self.tx_ip = diode_tx_ip # OT side (transmit)
self.rx_ip = diode_rx_ip # IT/DMZ side (receive)
self.port = historian_port
self.results = []
def test_forward_flow(self):
"""Verify data flows from OT (TX) to DMZ (RX) through diode."""
test_payload = f"DIODE_TEST_{datetime.now().isoformat()}"
try:
# Send test data to TX interface
sock = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)
sock.settimeout(5)
sock.sendto(test_payload.encode(), (self.tx_ip, self.port))
sock.close()
self.results.append({
"test": "forward_flow",
"status": "PASS",
"detail": f"Data sent to TX interface {self.tx_ip}:{self.port}",
})
except Exception as e:
self.results.append({
"test": "forward_flow",
"status": "FAIL",
"detail": f"Cannot reach TX interface: {e}",
})
def test_reverse_flow_blocked(self):
"""Verify reverse flow (DMZ to OT) is physically blocked by diode."""
try:
sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
sock.settimeout(3)
result = sock.connect_ex((self.tx_ip, self.port))
sock.close()
if result != 0:
self.results.append({
"test": "reverse_flow_blocked",
"status": "PASS",
"detail": "Reverse connection to OT side correctly rejected",
})
else:
self.results.append({
"test": "reverse_flow_blocked",
"status": "CRITICAL_FAIL",
"detail": "REVERSE FLOW POSSIBLE - Data diode bypass detected!",
})
except (socket.timeout, ConnectionRefusedError):
self.results.append({
"test": "reverse_flow_blocked",
"status": "PASS",
"detail": "Reverse connection timed out (expected with hardware diode)",
})
def test_historian_replication_latency(self):
"""Measure replication latency across the data diode."""
try:
sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
sock.settimeout(10)
start = time.time()
sock.connect((self.rx_ip, self.port))
latency = (time.time() - start) * 1000
sock.close()
status = "PASS" if latency < 1000 else "WARN"
self.results.append({
"test": "replication_latency",
"status": status,
"detail": f"Replication endpoint latency: {latency:.1f}ms",
})
except Exception as e:
self.results.append({
"test": "replication_latency",
"status": "FAIL",
"detail": f"Cannot reach RX historian: {e}",
})
def run_all_tests(self):
"""Run complete data diode validation suite."""
print("=" * 60)
print("DATA DIODE VALIDATION REPORT")
print("=" * 60)
self.test_forward_flow()
self.test_reverse_flow_blocked()
self.test_historian_replication_latency()
for r in self.results:
status_icon = "+" if r["status"] == "PASS" else "-"
print(f" [{status_icon}] {r['test']}: {r['status']}")
print(f" {r['detail']}")
return self.results
if __name__ == "__main__":
validator = DataDiodeValidator(
diode_tx_ip="10.30.1.100", # Operations zone TX
diode_rx_ip="172.16.1.100", # DMZ zone RX
)
validator.run_all_tests()
After implementation, validate the zone architecture by verifying that only authorized conduit traffic passes between zones and that all prohibited cross-zone paths are blocked.
# Validation test from Enterprise zone - should be blocked from reaching BPCS
nmap -sT -p 502,44818,102,4840 10.20.0.0/16 --reason
# Expected: All ports filtered/closed
# Validation test from Operations zone - read-only Modbus should work
python3 -c "
from pymodbus.client import ModbusTcpClient
client = ModbusTcpClient('10.20.1.10', port=502)
client.connect()
# Read should succeed
result = client.read_holding_registers(0, 10, slave=1)
print(f'Read test: {\"PASS\" if not result.isError() else \"FAIL\"}')
# Write should be blocked by firewall
result = client.write_register(0, 100, slave=1)
print(f'Write blocked: {\"PASS\" if result.isError() else \"FAIL - WRITE PERMITTED!\"}')
client.close()
"
# Verify data diode blocks reverse traffic
ping -c 3 10.30.1.100 # From DMZ to OT - should timeout
# Expected: 100% packet loss (hardware diode blocks ICMP)
| Term | Definition |
|---|---|
| Security Zone | A grouping of logical or physical assets that share common security requirements, as defined by IEC 62443-3-2 |
| Conduit | A logical grouping of communication channels connecting two or more zones, subject to common security policies |
| Security Level Target (SL-T) | The desired security level for a zone, ranging from SL 1 (casual violation) to SL 4 (state-sponsored attack) |
| Data Diode | Hardware-enforced unidirectional network gateway that physically prevents data from flowing in the reverse direction |
| Microsegmentation | Granular network segmentation at the device level, managing communication device-by-device based on roles and functions |
| Deep Packet Inspection (DPI) | Firewall capability to inspect industrial protocol payloads (Modbus function codes, OPC UA service calls) beyond Layer 4 |
| Defense in Depth | Layered security approach where multiple security controls protect assets at different levels of the architecture |
Context: A manufacturing plant operates all OT devices on a single VLAN (10.10.0.0/16) with no segmentation between PLCs, HMIs, historians, and the corporate network. An IEC 62443 gap assessment identified this as a critical finding requiring zone implementation.
Approach:
Pitfalls: Implementing zone firewalls without a complete traffic baseline will break unknown but legitimate communication paths. Scheduling zone cutover during production instead of maintenance windows risks process disruptions. Placing SIS controllers in the same zone as BPCS violates IEC 62443 safety system isolation requirements.
IEC 62443 Zone Implementation Report
=====================================
Facility: [Name]
Implementation Date: YYYY-MM-DD
Standard: IEC 62443-3-2/3-3
ZONE ARCHITECTURE:
Zone [ID]: [Name] (SL-T: [1-4])
Assets: [count]
Conduits: [list]
Controls: [firewall type, data diode, etc.]
CONDUIT CONFIGURATION:
Conduit [ID]: [Zone A] <-> [Zone B]
Protocols: [allowed protocols with direction]
Firewall Rules: [count allow / count deny]
DPI Enabled: Yes/No
VALIDATION RESULTS:
Cross-zone tests: [pass/fail count]
Prohibited path tests: [all blocked / exceptions]
Protocol enforcement: [function code filtering verified]