undermybelt Implementing Conduit Security for OT Remote Access
When to Use
- When replacing direct VPN connections from IT or vendors into OT control networks
- When implementing IEC 62443-compliant conduit architecture for remote access paths
- When deploying secure remote access for third-party vendor maintenance of ICS equipment
- When building approval-based access workflows for privileged OT system access
- When remediating audit findings about uncontrolled remote access to SCADA systems
Do not use for designing the overall Purdue Model segmentation (see implementing-purdue-model-network-segmentation), for deploying IT-only remote access solutions, or for configuring local console access to PLCs.
Prerequisites
- IT/OT DMZ (Level 3.5) deployed with dual-firewall architecture
- Jump server or privileged access management (PAM) platform (CyberArk, BeyondTrust)
- Multi-factor authentication (MFA) infrastructure for OT remote access users
- Session recording capability for compliance and forensic purposes
- Approval workflow system (ServiceNow, ticketing) for access requests
Workflow
Step 1: Design Conduit Architecture for Remote Access
# IEC 62443 Conduit Security Architecture for OT Remote Access
# All remote access terminates in DMZ - never passes through to OT directly
conduit_architecture:
remote_access_conduit:
conduit_id: "RA-001"
source_zone: "Enterprise IT (Level 4)"
destination_zone: "OT DMZ (Level 3.5)"
security_level_target: "SL3"
components:
external_gateway:
type: "VPN Concentrator"
location: "Enterprise DMZ"
ip: "10.200.1.10"
protocols: ["IPsec", "SSL-VPN"]
authentication: "MFA required (certificate + OTP)"
dmz_jump_server:
type: "Privileged Access Workstation"
location: "OT DMZ (Level 3.5)"
ip: "10.10.150.20"
os: "Windows Server 2022 (hardened)"
controls:
- "Local admin accounts disabled"
- "USB ports disabled"
- "Clipboard transfer disabled by default"
- "Session recording enabled (all keystrokes and screen)"
- "Maximum session duration: 4 hours"
- "Automatic logoff after 15 minutes idle"
- "Application whitelisting enforced"
ot_access_gateway:
type: "Industrial Remote Access Gateway"
location: "OT DMZ / Level 3 boundary"
ip: "10.10.150.25"
controls:
- "Only pre-approved destination IPs reachable"
- "Protocol-level filtering (RDP, SSH, VNC only)"
- "Time-limited sessions with automatic expiry"
- "Approval-based access (plant manager must authorize)"
data_flow:
- step: 1
description: "User authenticates via enterprise VPN with MFA"
source: "Remote user"
destination: "VPN concentrator"
protocol: "IPsec/SSL-VPN"
- step: 2
description: "User connects to jump server in OT DMZ"
source: "VPN tunnel"
destination: "DMZ jump server"
protocol: "RDP with NLA"
- step: 3
description: "From jump server, user accesses specific OT system"
source: "DMZ jump server"
destination: "Approved OT target"
protocol: "RDP/SSH/VNC"
condition: "Only after manager approval and within time window"
prohibited_flows:
- "Direct VPN tunnel from external to Level 1/2 OT devices"
- "Split tunneling allowing internet access during OT session"
- "File transfer from jump server to OT without scanning"
- "Persistent VPN connections (auto-reconnect disabled)"
vendor_access_conduit:
conduit_id: "VA-001"
source_zone: "Vendor External Network"
destination_zone: "OT DMZ (Level 3.5)"
security_level_target: "SL3"
workflow:
request:
- "Vendor submits access request via portal (24h advance)"
- "Request includes: purpose, target systems, duration, personnel"
- "Plant operations manager reviews and approves/rejects"
- "Time-limited credentials generated upon approval"
session:
- "Vendor connects via dedicated vendor VPN gateway"
- "MFA authentication (vendor receives OTP via SMS/app)"
- "Session lands on vendor-specific jump server (isolated from internal jump)"
- "All actions recorded (video + keystroke logging)"
- "OT engineer monitors vendor session in real-time"
termination:
- "Session auto-terminates at approved end time"
- "Credentials automatically revoked"
- "Session recording archived for 90 days"
- "Access log forwarded to SIEM"
Step 2: Implement Access Control and Monitoring
#!/usr/bin/env python3
"""OT Remote Access Conduit Manager.
Manages approval-based remote access to OT systems through
secure conduit architecture with session recording, MFA
enforcement, and time-limited access windows.
"""
import json
import sys
from datetime import datetime, timedelta
from typing import Dict, List, Optional
from enum import Enum
class AccessRequestStatus(Enum):
PENDING = "pending"
APPROVED = "approved"
REJECTED = "rejected"
ACTIVE = "active"
EXPIRED = "expired"
REVOKED = "revoked"
class RemoteAccessRequest:
"""Represents an OT remote access request."""
def __init__(self, requestor: str, requestor_type: str, purpose: str,
target_systems: List[str], duration_hours: int,
requested_start: str):
self.id = f"OT-RA-{datetime.now().strftime('%Y%m%d-%H%M%S')}"
self.requestor = requestor
self.requestor_type = requestor_type # "internal_engineer" or "vendor"
self.purpose = purpose
self.target_systems = target_systems
self.duration_hours = duration_hours
self.requested_start = requested_start
self.status = AccessRequestStatus.PENDING
self.created = datetime.now().isoformat()
self.approved_by = None
self.session_id = None
self.audit_trail = []
def approve(self, approver: str, conditions: str = ""):
"""Approve the access request."""
self.status = AccessRequestStatus.APPROVED
self.approved_by = approver
self.audit_trail.append({
"timestamp": datetime.now().isoformat(),
"action": "APPROVED",
"actor": approver,
"conditions": conditions,
})
def reject(self, rejector: str, reason: str):
"""Reject the access request."""
self.status = AccessRequestStatus.REJECTED
self.audit_trail.append({
"timestamp": datetime.now().isoformat(),
"action": "REJECTED",
"actor": rejector,
"reason": reason,
})
class OTConduitManager:
"""Manages OT remote access conduit security."""
def __init__(self):
self.access_requests: Dict[str, RemoteAccessRequest] = {}
self.active_sessions: Dict[str, dict] = {}
self.policy = self._load_policy()
def _load_policy(self) -> dict:
"""Load remote access policy."""
return {
"max_session_hours": 4,
"idle_timeout_minutes": 15,
"mfa_required": True,
"session_recording": True,
"clipboard_transfer": False,
"file_transfer": "scan_required",
"advance_notice_hours": 24,
"vendor_escort_required": True,
"prohibited_targets": ["SIS-*", "SAFETY-*"],
"allowed_protocols": ["RDP", "SSH", "VNC"],
"blocked_protocols": ["Telnet", "FTP", "SMB"],
}
def submit_request(self, request: RemoteAccessRequest) -> str:
"""Submit a new remote access request."""
# Validate against policy
violations = []
if request.duration_hours > self.policy["max_session_hours"]:
violations.append(
f"Duration {request.duration_hours}h exceeds maximum {self.policy['max_session_hours']}h"
)
for target in request.target_systems:
for prohibited in self.policy["prohibited_targets"]:
pattern = prohibited.replace("*", "")
if target.startswith(pattern):
violations.append(f"Target {target} is in prohibited list (safety systems)")
if violations:
print(f"[!] Policy violations found:")
for v in violations:
print(f" - {v}")
return ""
self.access_requests[request.id] = request
print(f"[+] Access request {request.id} submitted for approval")
return request.id
def list_pending_requests(self):
"""List all pending access requests for approval."""
pending = [r for r in self.access_requests.values()
if r.status == AccessRequestStatus.PENDING]
print(f"\n{'='*65}")
print("PENDING OT REMOTE ACCESS REQUESTS")
print(f"{'='*65}")
if not pending:
print(" No pending requests")
return
for req in pending:
print(f"\n Request: {req.id}")
print(f" Requestor: {req.requestor} ({req.requestor_type})")
print(f" Purpose: {req.purpose}")
print(f" Targets: {', '.join(req.target_systems)}")
print(f" Duration: {req.duration_hours} hours")
print(f" Start: {req.requested_start}")
print(f" Submitted: {req.created}")
def generate_audit_report(self):
"""Generate audit report of all remote access activity."""
print(f"\n{'='*65}")
print("OT REMOTE ACCESS AUDIT REPORT")
print(f"{'='*65}")
print(f"Report Date: {datetime.now().isoformat()}")
print(f"Total Requests: {len(self.access_requests)}")
status_counts = {}
for req in self.access_requests.values():
status = req.status.value
status_counts[status] = status_counts.get(status, 0) + 1
print(f"\nRequest Status:")
for status, count in status_counts.items():
print(f" {status}: {count}")
print(f"\nDetailed Audit Trail:")
for req in self.access_requests.values():
print(f"\n {req.id} - {req.requestor} ({req.requestor_type})")
print(f" Status: {req.status.value}")
print(f" Targets: {', '.join(req.target_systems)}")
for entry in req.audit_trail:
print(f" [{entry['timestamp']}] {entry['action']} by {entry['actor']}")
if __name__ == "__main__":
manager = OTConduitManager()
# Vendor access request
vendor_req = RemoteAccessRequest(
requestor="John Smith - Siemens Field Service",
requestor_type="vendor",
purpose="Annual PLC firmware update for S7-1500 controllers",
target_systems=["PLC-REACTOR-01", "PLC-REACTOR-02"],
duration_hours=3,
requested_start="2025-03-15T08:00:00",
)
req_id = manager.submit_request(vendor_req)
if req_id:
manager.list_pending_requests()
# Simulate approval
manager.access_requests[req_id].approve(
approver="Plant Manager - Jane Doe",
conditions="OT engineer must shadow the vendor session",
)
manager.generate_audit_report()
Key Concepts
| Term | Definition |
|---|---|
| Conduit | IEC 62443 controlled communication path between security zones with defined security policies |
| Jump Server | Hardened intermediary server in the DMZ through which all remote OT access must transit |
| Session Recording | Capture of all screen activity, keystrokes, and commands during a remote access session for audit |
| Approval-Based Access | Workflow requiring plant operations manager authorization before remote access credentials are activated |
| Vendor Escort | Practice of having an internal OT engineer monitor vendor remote sessions in real time |
| Break-Glass Access | Emergency access procedure bypassing normal approval workflow for critical situations |
Output Format
OT REMOTE ACCESS CONDUIT REPORT
==================================
Date: YYYY-MM-DD
CONDUIT STATUS:
Internal Access Conduit: [Active/Inactive]
Vendor Access Conduit: [Active/Inactive]
ACCESS REQUESTS (Last 30 Days):
Submitted: [count]
Approved: [count]
Rejected: [count]
Average Session Duration: [hours]
POLICY COMPLIANCE:
MFA Enforcement: [100%]
Session Recording: [100%]
Time-Limited Sessions: [compliance %]
Prohibited Target Attempts: [count blocked]