Securing Remote Access To Ot Environment

保护OT环境的远程访问

适用场景

• 为OT环境实施或升级远程访问架构时
• 需要远程访问OT系统进行支持和维护的供应商入驻时
• 实施CIP-005-7 R2中包括MFA在内的远程访问管理要求时
• 用安全跳板服务器架构替换对OT网络的旧版直接VPN访问时
• 响应涉及对工业控制系统未授权远程访问的事件时

不适用于保护没有OT组件的纯IT远程访问、为企业员工配置VPN（参见通用VPN指南），或OT设施的物理访问控制。

前置条件

• 企业IT网络与OT网络之间的DMZ基础设施（第3.5层）
• 跳板服务器/堡垒主机平台（CyberArk、BeyondTrust或加固的Windows/Linux服务器）
• 多因素认证解决方案（Duo、RSA SecurID、YubiKey、智能卡）
• 用于审计跟踪合规的会话记录功能
• 仅允许通过DMZ中间系统进行远程访问的防火墙规则

工作流程

步骤 1：设计安全远程访问架构

在DMZ中实施具有中间系统的深度防御远程访问架构，防止外部用户与OT系统之间的任何直接网络连接。

# OT远程访问架构
# 关键原则：外部网络到OT系统无直接连接

architecture:
  external_access_point:
    location: "面向互联网的防火墙"
    service: "VPN网关（IKEv2/IPsec或SSL VPN）"
    authentication: "证书 + MFA（CIP-005-7 R2.4）"
    controls:
      - "供应商访问的源IP白名单"
      - "基于时间的访问窗口"
      - "带宽速率限制"

  dmz_intermediate_system:
    location: "第3.5层DMZ"
    platform: "CyberArk特权访问安全或加固的跳板服务器"
    function: "会话代理——终止外部连接，发起新的内部连接"
    controls:
      - "所有会话在跳板服务器终止（不直通）"
      - "带键盘记录的会话录制"
      - "剪贴板和文件传输限制"
      - "不活跃30分钟后会话超时"
      - "每用户并发会话限制"

  ot_internal_access:
    location: "第3层/第2层OT网络"
    method: "跳板服务器向OT系统发起RDP/SSH/VNC连接"
    controls:
      - "防火墙仅允许跳板服务器IP到达OT"
      - "协议受限（RDP 3389、SSH 22、VNC 5900）"
      - "按用户角色限定目标"

  vendor_access:
    description: "第三方供应商远程访问"
    additional_controls:
      - "供应商账户默认禁用；按请求启用"
      - "时间限制的访问窗口（按会话启用/禁用）"
      - "OT操作员必须在供应商会话期间陪同"
      - "OT安全团队实时监控会话"
      - "无持久凭据——使用一次性访问令牌"

# 网络流向:
# 用户 -> VPN -> 防火墙 -> DMZ跳板服务器 -> 内部防火墙 -> OT系统
# （两个独立的已认证连接；无直接路由）

步骤 2：配置带特权访问管理的跳板服务器

在DMZ中部署和加固跳板服务器，配置会话管理、记录和基于角色的访问控制。

#!/usr/bin/env python3
"""OT远程访问会话管理器。

管理对OT环境的授权远程访问会话，
包括会话创建、监控、录制和终止。
与PAM解决方案集成以进行凭据存管。
"""

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 = ""
    max_duration_minutes: int = 120
    recording_path: str = ""
    actions_logged: list = field(default_factory=list)


class OTRemoteAccessManager:
    """管理OT环境的远程访问会话。"""

    def __init__(self):
        self.sessions = {}
        self.active_sessions = {}
        self.access_policies = {}
        self.audit_log = []

    def define_access_policy(self, role, allowed_targets, protocols, max_duration):
        """为用户角色定义访问策略。"""
        self.access_policies[role] = {
            "allowed_targets": allowed_targets,
            "allowed_protocols": protocols,
            "max_duration_minutes": max_duration,
            "requires_co_attendance": role == UserRole.VENDOR,
            "requires_approval": role == UserRole.VENDOR,
        }

    def request_session(self, user_id, user_role, source_ip,
                        target_system, target_ip, protocol, purpose):
        """请求新的远程访问会话。"""
        # 生成唯一会话ID
        session_id = hashlib.sha256(
            f"{user_id}{target_ip}{datetime.now().isoformat()}".encode()
        ).hexdigest()[:16]

        # 检查访问策略
        policy = self.access_policies.get(user_role)
        if not policy:
            return None, "该角色未定义访问策略"

        if target_system not in policy["allowed_targets"]:
            self._audit("ACCESS_DENIED", user_id, target_system,
                       f"目标不在角色 {user_role} 的允许列表中")
            return None, f"角色 {user_role} 未授权访问目标 {target_system}"

        if protocol not in policy["allowed_protocols"]:
            self._audit("ACCESS_DENIED", user_id, target_system,
                       f"角色 {user_role} 不允许协议 {protocol}")
            return None, f"未授权使用协议 {protocol}"

        session = RemoteAccessSession(
            session_id=session_id,
            user_id=user_id,
            user_role=user_role,
            source_ip=source_ip,
            target_system=target_system,
            target_ip=target_ip,
            protocol=protocol,
            purpose=purpose,
            max_duration_minutes=policy["max_duration_minutes"],
            created_at=datetime.now().isoformat(),
        )

        # 供应商会话需要审批
        if policy.get("requires_approval"):
            session.state = SessionState.PENDING_APPROVAL
        else:
            session.state = SessionState.APPROVED

        self.sessions[session_id] = session
        self._audit("SESSION_REQUESTED", user_id, target_system, purpose)

        return session_id, "会话已创建"

    def approve_session(self, session_id, approver_id):
        """审批待审批的供应商会话。"""
        session = self.sessions.get(session_id)
        if not session:
            return False, "未找到会话"
        if session.state != SessionState.PENDING_APPROVAL:
            return False, "会话不在待审批状态"

        session.state = SessionState.APPROVED
        session.approved_by = approver_id
        self._audit("SESSION_APPROVED", approver_id, session.target_system,
                    f"已审批 {session.user_id} 的会话 {session_id}")
        return True, "会话已审批"

    def activate_session(self, session_id, mfa_token):
        """MFA验证后激活已审批的会话。"""
        session = self.sessions.get(session_id)
        if not session or session.state != SessionState.APPROVED:
            return False, "会话未获审批"

        # 验证MFA（简化版——实际实现调用MFA提供商）
        session.mfa_verified = True
        session.state = SessionState.ACTIVE
        session.started_at = datetime.now().isoformat()
        session.recording_path = f"/recordings/{session_id}_{datetime.now().strftime('%Y%m%d')}.mp4"

        self.active_sessions[session_id] = session
        self._audit("SESSION_ACTIVATED", session.user_id, session.target_system,
                    f"MFA已验证，录制到 {session.recording_path}")

        return True, "会话已激活"

    def terminate_session(self, session_id, reason="manual"):
        """终止活跃会话。"""
        session = self.active_sessions.pop(session_id, None)
        if not session:
            session = self.sessions.get(session_id)
        if not session:
            return False

        session.state = SessionState.TERMINATED
        session.ended_at = datetime.now().isoformat()
        self._audit("SESSION_TERMINATED", session.user_id, session.target_system, reason)
        return True

    def check_expired_sessions(self):
        """终止超过最大时长的会话。"""
        now = datetime.now()
        expired = []
        for sid, session in list(self.active_sessions.items()):
            started = datetime.fromisoformat(session.started_at)
            if (now - started).total_seconds() > session.max_duration_minutes * 60:
                self.terminate_session(sid, "超过最大时长")
                expired.append(sid)
        return expired

    def _audit(self, event_type, user_id, target, detail):
        """写入审计日志。"""
        self.audit_log.append({
            "timestamp": datetime.now().isoformat(),
            "event": event_type,
            "user": user_id,
            "target": target,
            "detail": detail,
        })

    def generate_report(self):
        """生成远程访问会话报告。"""
        report = []
        report.append("=" * 70)
        report.append("OT远程访问会话报告")
        report.append(f"日期: {datetime.now().isoformat()}")
        report.append("=" * 70)

        # 会话摘要
        total = len(self.sessions)
        active = sum(1 for s in self.sessions.values() if s.state == SessionState.ACTIVE)
        report.append(f"\n总会话数: {total}")
        report.append(f"活跃会话数: {active}")

        # 活跃会话详情
        if self.active_sessions:
            report.append("\n活跃会话:")
            for sid, s in self.active_sessions.items():
                report.append(f"  [{sid[:8]}] {s.user_id} ({s.user_role})")
                report.append(f"    目标: {s.target_system} ({s.target_ip})")
                report.append(f"    开始: {s.started_at}")
                report.append(f"    MFA: {'已验证' if s.mfa_verified else '未验证'}")

        return "\n".join(report)


if __name__ == "__main__":
    manager = OTRemoteAccessManager()

    # 定义策略
    manager.define_access_policy(
        UserRole.OT_ENGINEER,
        ["HMI-01", "HMI-02", "EWS-01", "HISTORIAN-01"],
        ["RDP", "SSH"],
        max_duration=240,
    )
    manager.define_access_policy(
        UserRole.VENDOR,
        ["DCS-EWS-01"],
        ["RDP"],
        max_duration=120,
    )

    # 请求供应商会话
    sid, msg = manager.request_session(
        "vendor_honeywell_01", UserRole.VENDOR,
        "203.0.113.50", "DCS-EWS-01", "10.30.1.20",
        "RDP", "DCS固件更新，变更请求 CR-2026-0045")
    print(f"会话请求: {msg} ({sid})")

    if sid:
        manager.approve_session(sid, "ot_manager_01")
        manager.activate_session(sid, "123456")
        print(manager.generate_report())

核心概念

工具和系统

• CyberArk特权访问安全: 企业PAM，具备OT远程访问的会话管理、凭据存管和录制功能
• BeyondTrust特权远程访问（PRA）: 专为目的设计的远程访问解决方案，具备会话记录和细粒度访问策略
• Claroty安全远程访问（SRA）: OT专用远程访问解决方案，具备协议感知会话控制
• Duo Security: MFA提供商，支持推送通知、硬件令牌和生物识别用于OT访问验证

输出格式

OT远程访问安全报告
===================================
活跃会话: [N]
待审批: [N]
今日会话: [N]

MFA合规性:
  所有会话MFA已验证: [是/否]
  无MFA的会话: [N]

供应商访问:
  活跃供应商会话: [N]
  已陪同: [N]
  已录制: [N]