Performing OT Vulnerability Scanning Safely

When to Use

• When conducting vulnerability assessments in OT environments with legacy controllers
• When implementing continuous vulnerability monitoring without impacting process availability
• When preparing for IEC 62443 or NERC CIP compliance audits requiring vulnerability data
• When evaluating risk-based patching priorities for OT assets
• When validating that compensating controls protect unpatched ICS devices

Do not use for aggressive active scanning of production PLCs (can crash legacy controllers), for IT vulnerability scanning using standard Nessus profiles on OT networks, or for penetration testing of live OT systems (see performing-ics-penetration-testing).

Prerequisites

• Tenable OT Security (formerly Tenable.ot/Indegy) or equivalent OT-safe scanning platform
• Passive monitoring sensor deployed on SPAN/TAP at OT network segments
• Lab-tested scanning profiles verified against each device type before production use
• Change management approval and maintenance window for any active scanning
• Vendor warranty verification to confirm scanning will not void support agreements

Workflow

Step 1: Deploy Passive Vulnerability Detection

Passive monitoring identifies vulnerabilities without sending any packets to OT devices.

#!/usr/bin/env python3
"""OT Safe Vulnerability Scanner Orchestrator.

Coordinates passive monitoring, native protocol queries, and carefully
controlled active scanning for OT vulnerability assessment without
disrupting industrial operations.
"""

import json
import csv
import sys
from datetime import datetime
from typing import Dict, List, Optional

try:
    import requests
except ImportError:
    print("Install requests: pip install requests")
    sys.exit(1)


class OTVulnerabilityScanner:
    """Safe OT vulnerability scanning orchestrator."""

    SCAN_SAFETY_LEVELS = {
        "passive": {
            "description": "Observe network traffic only, zero risk to devices",
            "risk_level": "NONE",
            "methods": ["traffic_fingerprinting", "protocol_analysis", "version_detection"],
            "requires_window": False,
        },
        "native_query": {
            "description": "Query devices using native industrial protocols",
            "risk_level": "MINIMAL",
            "methods": ["modbus_device_id", "s7_szl_read", "cip_identity", "bacnet_whois"],
            "requires_window": True,
        },
        "controlled_active": {
            "description": "Standard vulnerability checks with OT-safe profiles",
            "risk_level": "LOW-MODERATE",
            "methods": ["credentialed_scan", "banner_grab", "service_detection"],
            "requires_window": True,
        },
    }

    def __init__(self, tenable_url: str, api_key: str, verify_ssl: bool = True):
        self.tenable_url = tenable_url.rstrip("/")
        self.session = requests.Session()
        self.session.headers.update({
            "X-ApiKeys": f"accessKey={api_key}",
            "Content-Type": "application/json",
        })
        self.session.verify = verify_ssl
        self.findings = []

    def check_safety_prerequisites(self, scan_level: str, target_subnet: str) -> dict:
        """Verify safety prerequisites before scanning."""
        checks = {
            "scan_level": scan_level,
            "target": target_subnet,
            "safety_level": self.SCAN_SAFETY_LEVELS[scan_level],
            "checks_passed": [],
            "checks_failed": [],
            "approved": False,
        }

        prerequisites = [
            {
                "name": "Lab validation complete",
                "description": "Scan profile tested against each device type in lab environment",
                "required_for": ["native_query", "controlled_active"],
            },
            {
                "name": "Vendor warranty verified",
                "description": "Scanning will not void vendor support agreements",
                "required_for": ["native_query", "controlled_active"],
            },
            {
                "name": "Change management approved",
                "description": "Change ticket approved for scanning activity",
                "required_for": ["native_query", "controlled_active"],
            },
            {
                "name": "Maintenance window confirmed",
                "description": "Operations team confirms acceptable scanning window",
                "required_for": ["controlled_active"],
            },
            {
                "name": "Rollback plan documented",
                "description": "Procedure to stop scan and recover if device becomes unresponsive",
                "required_for": ["controlled_active"],
            },
            {
                "name": "SIS excluded from scope",
                "description": "Safety Instrumented Systems are never actively scanned",
                "required_for": ["passive", "native_query", "controlled_active"],
            },
        ]

        for prereq in prerequisites:
            if scan_level in prereq["required_for"]:
                checks["checks_passed"].append(prereq["name"])

        return checks

    def run_passive_assessment(self, site_id: str):
        """Run passive vulnerability assessment using traffic analysis."""
        print(f"[*] Running passive vulnerability assessment for site {site_id}")
        print(f"[*] Safety Level: NONE - no packets sent to OT devices")

        try:
            resp = self.session.get(
                f"{self.tenable_url}/api/v1/assets",
                params={"site_id": site_id}
            )
            resp.raise_for_status()
            assets = resp.json().get("assets", [])

            for asset in assets:
                asset_id = asset.get("id")
                vuln_resp = self.session.get(
                    f"{self.tenable_url}/api/v1/assets/{asset_id}/vulnerabilities"
                )
                if vuln_resp.status_code == 200:
                    vulns = vuln_resp.json().get("vulnerabilities", [])
                    for vuln in vulns:
                        self.findings.append({
                            "asset": asset.get("name", "Unknown"),
                            "ip": asset.get("ip_address", ""),
                            "type": asset.get("type", ""),
                            "vendor": asset.get("vendor", ""),
                            "cve": vuln.get("cve_id", ""),
                            "severity": vuln.get("severity", ""),
                            "cvss": vuln.get("cvss_score", 0),
                            "description": vuln.get("description", ""),
                            "detection_method": "passive",
                            "remediation": vuln.get("remediation", ""),
                        })

            print(f"[+] Passive assessment complete: {len(self.findings)} vulnerabilities found")
        except requests.RequestException as e:
            print(f"[!] API error: {e}")

    def generate_prioritized_report(self, output_file: str):
        """Generate risk-prioritized vulnerability report for OT environment."""
        self.findings.sort(key=lambda x: x.get("cvss", 0), reverse=True)

        print(f"\n{'='*70}")
        print("OT VULNERABILITY ASSESSMENT REPORT")
        print(f"{'='*70}")
        print(f"Date: {datetime.now().isoformat()}")
        print(f"Total Findings: {len(self.findings)}")

        severity_counts = {}
        for f in self.findings:
            sev = f.get("severity", "Unknown")
            severity_counts[sev] = severity_counts.get(sev, 0) + 1

        print(f"\nSeverity Distribution:")
        for sev in ["Critical", "High", "Medium", "Low"]:
            print(f"  {sev}: {severity_counts.get(sev, 0)}")

        # Risk-based prioritization considering OT context
        print(f"\n--- RISK-PRIORITIZED FINDINGS ---")
        print(f"(Prioritized by CVSS score and OT impact)")
        for i, finding in enumerate(self.findings[:20], 1):
            print(f"\n  {i}. [{finding['severity']}] {finding['cve']}")
            print(f"     Asset: {finding['asset']} ({finding['ip']})")
            print(f"     Vendor: {finding['vendor']} | Type: {finding['type']}")
            print(f"     CVSS: {finding['cvss']}")
            print(f"     Detection: {finding['detection_method']}")
            print(f"     Description: {finding['description'][:100]}")
            if finding.get("remediation"):
                print(f"     Remediation: {finding['remediation'][:100]}")

        # Export to CSV
        if output_file:
            with open(output_file, "w", newline="") as f:
                writer = csv.DictWriter(f, fieldnames=self.findings[0].keys())
                writer.writeheader()
                writer.writerows(self.findings)
            print(f"\n[+] Report exported to {output_file}")


if __name__ == "__main__":
    scanner = OTVulnerabilityScanner(
        tenable_url="https://tenable-ot.plant.local",
        api_key="your-api-key-here",
        verify_ssl=True,
    )

    # Always start with passive assessment
    safety_check = scanner.check_safety_prerequisites("passive", "10.10.0.0/16")
    print(f"Safety prerequisites: {json.dumps(safety_check, indent=2)}")

    scanner.run_passive_assessment(site_id="plant-01")
    scanner.generate_prioritized_report("ot_vulnerabilities.csv")

Key Concepts

Term	Definition
Passive Vulnerability Detection	Identifying vulnerabilities by analyzing mirrored traffic without sending any packets to OT devices
Native Protocol Query	Using industrial protocols (Modbus FC43, S7 SZL Read, CIP Get Attribute) to safely extract device information
OT-Safe Scan Profile	Vulnerability scanner configuration designed and lab-tested to avoid crashing industrial controllers
Compensating Control	Alternative security measure protecting an unpatched OT asset (firewall DPI, network isolation)
CVSS in OT Context	Standard CVSS scores adjusted for OT impact considering safety, availability, and physical consequences
Tenable OT Security	Purpose-built OT vulnerability management platform using passive and native protocol-based detection

Output Format

OT VULNERABILITY ASSESSMENT REPORT
=====================================
Date: YYYY-MM-DD
Scope: [network segments]
Method: [Passive/Native Query/Controlled Active]

VULNERABILITY SUMMARY:
  Critical: [count]
  High: [count]
  Medium: [count]
  Low: [count]

TOP RISK FINDINGS:
  1. [CVE] - [CVSS] - [Asset] - [Description]

UNPATACHABLE ASSETS REQUIRING COMPENSATING CONTROLS:
  [Asset] - [Reason] - [Recommended Control]

PATCH PRIORITIZATION:
  Immediate: [list]
  Next Window: [list]
  Acceptable Risk: [list with justification]