Passive vs Active Scanning for IoT: What is the Difference and Why it Matters

As connected devices continue to proliferate across all industries, understanding how to safeguard these devices against critical vulnerabilities becomes crucial. Data show that 56% of Internet of Things (IoT) devices are more vulnerable to malware and cyberattacks due to their older operating systems. Further complicating the matter, these devices are more challenging to secure than traditional IT infrastructure because of those old, end-of-life (EOL) operating systems that the manufacturer may no longer support. 

Many organizations leverage network vulnerability scanners to safeguard their network from cyber risks. However, these technologies function differently within the IoT ecosystem. When businesses understand the difference between passive and active scanning, they can make an informed decision about the best risk mitigation and reduction approach within their network.

What is a Network Vulnerability Scanner?

Over the past several years, the number of critical vulnerabilities discovered has sharply increased. Vulnerabilities are identified by common vulnerabilities and exposures (CVE) and scored using the common vulnerability scoring system (CVSS). The ongoing surge of CVEs impacts both traditional IT and IoT devices, and patching every vulnerability is simply untenable as the number of vulnerabilities discovered yearly continues to climb. For IoT devices, not every vulnerability is a path to exploit, and those that target EoL software may not even have patches, making compensating controls and monitoring the best solution.

In general, passive scanning discreetly gathers data without interacting with devices, while active scanning can probe devices, offering a more hands-on approach. At a base level, vulnerability scanners inventory everything connected to an organization’s network, capturing valuable data on what devices may be vulnerable to compromise. From here, the similarities deviate:

• Passive scanning observes network traffic and collects information about systems and endpoints. Passive scanners are useful for monitoring in-use devices.
• Active scanning sends requests to devices and examines the responses. Active scanners can help resolve in-progress security incidents or monitor for anomalous behavior that could indicate an attack.

Advantages and Disadvantages of Active vs. Passive Scanning in IoT Environments

While there is no one-size-fits-all rule for monitoring the health of an organization’s network, passive scanning is generally useful for continuous monitoring, and active scanning is well suited for full vulnerability assessments or assets that are known to continue to function when receiving scanning traffic. 

However, both techniques have advantages and disadvantages that organizations should be mindful of:

Passive Scanning

Passive scanning is just that—passive. It doesn’t generate network traffic or interact with a device in any way, making it less likely to interfere with critical processes or overload the network with unwanted traffic. As a result, passive scanners are safe to monitor legacy and unpatched IoT or operational technology (OT) devices. Furthermore, OT environments operate within very strictly controlled parameters and may be programmed to ignore active scanners, which makes passive scanners a better choice for monitoring these sorts of networks.

Because passive scanning only detects what’s already happening on the network, it can be slow to detect information from devices that have minimal or infrequent network traffic, which can limit security teams’ visibility into the network. Passive scanners also cannot actively test devices for specific vulnerabilities.

Active Scanning

In direct contrast, active scanners don’t just detect devices from traffic, they make inquiries via well-known network management protocols like SNMP or device-specific APIs. To do this, active scanners directly probe devices by sending network requests and testing configurations. Active scanners may sometimes be referred to as checking the “health” of online systems because they can directly interact with devices. As a result, active scanners are beneficial for identifying misconfigurations.

Of course, this means that active scanners generate network traffic, and when they make requests for IoT devices, there can be unexpected results. Low-power devices with limited processing power can crash or go offline as a result of active scans. Depending on the IoT device, this could potentially disrupt other processes on the network. Many IoT devices run EoL software as they were designed to be operational longer than an operating system’s typical lifecycle; as a result, teams that leverage active scanners should consider how to appropriately harden the device against threats while maintaining stability.

When to Use Passive vs. Active Scanning in IoT Ecosystems

Both passive and active scanning have their place in a security team’s toolkit, but neither is a panacea against cyber threats—especially vulnerabilities. A business operating multiple IoT security cameras may use passive scanners to monitor traffic to and from the cameras, and active scanners can detect and alert if the cameras become operational at odd hours or start sending data to unknown devices, as it could be an indicator of compromise.  

Instead, organizations need to take a holistic view of risk within their IoT ecosystem and prioritize remediating the highest risks for the most vulnerable devices. Through this lens, it no longer becomes a matter of whether passive vs. active scanning is more effective and instead becomes a question of how to get the information needed to take mitigating actions to reduce a device’s risk profile. Understanding risk at the device level begins with leveraging an IoT security platform to create a comprehensive asset inventory of all IoT devices, their known configurations, behaviors, and vulnerability status. 

From here, organizations can gain risk-based insights into vulnerability status and make decisions about which vulnerabilities pose the greatest risk and require immediate attention. Vulnerability mitigation strategies should always be tailored to the organization and its unique operating environment.

The Asimily Approach to IoT Device Scanning

The Asimily platform is designed expressly with IoT risk mitigation in mind, and we take a different approach to vulnerability management. We know traditional methodologies are inexact because they lack context, and security teams need more insights to secure their IoT ecosystem. Context can mean the importance of a device or its true susceptibility to an exploit as the customer has deployed and configured it.

The Asimily platform offers organizations the depth and breadth of capability needed to build a robust inventory of all IoT devices and understand the specific context that may result in the device being vulnerable. 

After all, with over 40,000 vulnerabilities discovered last year, even the most diligent teams can’t address every vulnerability. Let Asmily give your team the information they need to make proactive risk mitigation and management decisions that ensure uptime and create a stronger security posture. 

Interested in learning more? Check out our platform overview.