Securing Remote Access to OT Environment

When to Use

• When implementing or upgrading remote access architecture for OT environments
• When onboarding vendors who require remote access to OT systems for support and maintenance
• When implementing CIP-005-7 R2 requirements for remote access management including MFA
• When replacing legacy direct VPN access to OT networks with a secure jump server architecture
• When responding to an incident involving unauthorized remote access to industrial control systems

Do not use for securing IT-only remote access without OT components, for configuring VPN for corporate workers (see general VPN guides), or for physical access control to OT facilities.

Prerequisites

• DMZ infrastructure (Level 3.5) between corporate IT and OT networks
• Jump server/bastion host platform (CyberArk, BeyondTrust, or hardened Windows/Linux server)
• Multi-factor authentication solution (Duo, RSA SecurID, YubiKey, smart cards)
• Session recording capability for audit trail compliance
• Firewall rules permitting remote access only through the DMZ intermediate system

Workflow

Step 1: Design Secure Remote Access Architecture

Implement a defense-in-depth remote access architecture with an intermediate system in the DMZ that prevents any direct network connectivity between external users and OT systems.

# OT Remote Access Architecture
# Key principle: NO direct connection from external networks to OT systems

architecture:
  external_access_point:
    location: "Internet-facing firewall"
    service: "VPN gateway (IKEv2/IPsec or SSL VPN)"
    authentication: "Certificate + MFA (CIP-005-7 R2.4)"
    controls:
      - "Source IP allowlisting for vendor access"
      - "Time-based access windows"
      - "Bandwidth rate limiting"

  dmz_intermediate_system:
    location: "Level 3.5 DMZ"
    platform: "CyberArk Privileged Access Security or hardened jump server"
    function: "Session broker - terminates external connection, initiates new internal connection"
    controls:
      - "All sessions terminate at jump server (no pass-through)"
      - "Session recording with keystroke logging"
      - "Clipboard and file transfer restrictions"
      - "Session timeout after 30 minutes inactivity"
      - "Concurrent session limits per user"

  ot_internal_access:
    location: "Level 3 / Level 2 OT network"
    method: "Jump server initiates RDP/SSH/VNC to OT systems"
    controls:
      - "Firewall allows only jump server IP to reach OT"
      - "Protocol restricted (RDP 3389, SSH 22, VNC 5900)"
      - "Destination-specific per user role"

  vendor_access:
    description: "Third-party vendor remote access"
    additional_controls:
      - "Vendor account disabled by default; enabled on request"
      - "Time-limited access windows (enable/disable per session)"
      - "OT operator must co-attend vendor sessions"
      - "Real-time session monitoring by OT security"
      - "No persistent credentials - one-time access tokens"

# Network flow:
# User -> VPN -> Firewall -> DMZ Jump Server -> Internal FW -> OT System
# (Two separate authenticated connections; no direct routing)

Step 2: Configure Jump Server with Privileged Access Management

Deploy and harden the jump server in the DMZ with session management, recording, and role-based access controls.

#!/usr/bin/env python3
"""OT Remote Access Session Manager.

Manages authorized remote access sessions to OT environments
including session creation, monitoring, recording, and termination.
Integrates with PAM solutions for credential vaulting.
"""

import json
import hashlib
import sys
from dataclasses import dataclass, field, asdict
from datetime import datetime, timedelta
from enum import Enum


class SessionState(str, Enum):
    PENDING_APPROVAL = "pending_approval"
    APPROVED = "approved"
    ACTIVE = "active"
    TERMINATED = "terminated"
    EXPIRED = "expired"
    DENIED = "denied"


class UserRole(str, Enum):
    OT_OPERATOR = "ot_operator"
    OT_ENGINEER = "ot_engineer"
    VENDOR = "vendor"
    SECURITY_ANALYST = "security_analyst"


@dataclass
class RemoteAccessSession:
    session_id: str
    user_id: str
    user_role: str
    source_ip: str
    target_system: str
    target_ip: str
    protocol: str
    purpose: str
    state: str = SessionState.PENDING_APPROVAL
    mfa_verified: bool = False
    approved_by: str = ""
    created_at: str = ""
    started_at: str = ""
    ended_at: str = ""

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