🚨 “Defender for IoT Drops Passive Scanning — Sensor-Based Security Is Now Mandatory”

Microsoft is sunsetting a key feature that many network admins didn’t even realize they were leaning on: Defender for IoT’s passive network scanning and vulnerability detection for unmanaged infrastructure devices. If you manage firewalls, switches, access points, UPS systems, or anything else with an IP address but no agent, this change affects you.

Let’s get into what’s going away, why it matters, and what you should do now before visibility vanishes.

---

🔚 What’s Being Retired?

As of October 2024, Microsoft is ending support for these features in Defender for IoT:

• Passive network scanning
• Device fingerprinting and profiling
• Vulnerability detection for unmanaged infrastructure
• Integration with Defender Vulnerability Management (DVM)

These capabilities gave IT teams visibility into non-Windows, non-agent-capable devices. That includes everything from your Cisco switches and SonicWall firewalls to your APC UPS units, VoIP phones, badge readers, and IoT sensor hubs.

No agent? No problem — until now.

---

🧱 Infrastructure Is More Than Servers

Modern networks are full of “smart” but unmanaged gear:

• Firewalls and routers with web interfaces and firmware
• Switches with SNMP and management VLANs
• Wireless access points, often cloud-managed but still vulnerable
• UPS devices running embedded Linux and often neglected
• Building automation systems, like HVAC or door controllers

These are not monitored by antivirus, EDR, or Intune. Defender for IoT filled the gap by passively sniffing traffic, profiling devices, identifying firmware versions, and flagging known vulnerabilities. That’s gone — unless you deploy sensors.

---

⚠️ Real-World Risk: Now You’re Blind

Without this scanning:

• You won’t know if that old Fortinet firewall still has that 2021 RCE bug
• You won’t see new rogue devices plugged into your network
• You won’t get alerts about outdated firmware or default credentials

And let’s be honest: no one is manually tracking firmware CVEs on every switch and UPS. That’s what tools like Defender for IoT were doing in the background.

---

💡 What Microsoft Wants: Move to Sensor-Based Monitoring

Microsoft wants you to transition to sensor-based deployments of Defender for IoT. Here’s how to do it:

---

🧭 How to Set Up a Sensor-Based Deployment

This is not plug-and-play — but it’s doable if you’re serious about visibility.

1. Plan Your Sensor Locations

• Sensors should sit on SPAN or mirror ports that capture traffic from core switches, firewalls, or OT VLANs.
• Don’t span trunk ports unless you know what you’re doing — it can flood the sensor or miss important broadcast domains.

2. Deploy the Sensor

You can use:

• Azure Defender for IoT Sensor (software VM) — available as an OVA/ISO to deploy in Hyper-V, VMware, or Azure
• Hardware appliances — sold through Microsoft partners (expensive, but purpose-built)
• Cloud-connected sensors for remote sites

3. Connect to Azure

• Use the Azure portal to onboard the sensor into the Defender for IoT workspace
• Configure telemetry forwarding to Microsoft Sentinel if you want SIEM correlation
• Make sure firewall rules and outbound ports are open for communication to Defender backends

4. Tune Your Detection Rules

• Customize detection policies per VLAN/device type
• Suppress known benign behaviors to avoid alert fatigue
• Enable threat intelligence feeds if you’re licensed

5. Map Network Zones and Assets

• Label your infrastructure — “Core Switch,” “UPS Rack,” “Building HVAC”
• Set up zones and asset groups so alerts are more meaningful

---

🧠 Things to Know Before You Start

• You’ll need SPAN-capable switches (not all cheap ones support this)
• You may need dedicated NICs or VLANs for traffic mirroring
• Don’t assume this is “set it and forget it” — sensors need tuning and review

And of course, this only gives you visibility into what the sensor can see — isolated branches or wireless-only segments might still be dark.

---

✅ What You Should Do Now

Here’s your action list if you want to stay protected:

1. Audit your current Defender for IoT usage
2. Decide if sensor deployment is worth it in your environment
3. If not — look for an alternative scanning tool (RunZero, Nessus, Qualys, etc.)
4. Update your vulnerability management plan for unmanaged devices
5. Push vendors for automated firmware alerting and update tools

---

🔐 Final Word: You Own the Risk Now

This EOL decision takes away a helpful safety net. Whether or not you choose to stick with Microsoft’s new approach, don’t ignore the gap this leaves.

Unmanaged devices are still part of your infrastructure — and attackers know they’re usually overlooked. You can’t patch what you can’t see.

If you’re not replacing this visibility with something else, you’re not secure. You’re just lucky — until you’re not.