Master Your Security Foundation: Know Your Devices

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Knowing what assets you have is arguably the single most important security control. If you don’t know about a server, desktop, laptop, mobile device or network device, how can you manage and secure it? For that matter, what about cloud instances, virtual machines, and containers?

Fewer than 50% of surveyed organizations have implemented automated controls to inventory the systems and devices connected to their networks

In Q4 of last year, Tenable and the Center for Internet Security (CIS) conducted a survey of 319 IT security decision makers at companies with more than 100 employees. We found that fewer than 50% of the surveyed organizations have implemented automated controls to inventory the systems and devices connected to their networks. I was alarmed by such low control adoption because, as the following table indicates, knowing what is on your network is an important control in virtually all security frameworks and compliance standards.


“Know What you Have” Control Objective


Maintain an inventory of systems that are in scope for PCI DSS.

NIST Cybersecurity Framework

Physical devices and systems are inventoried.

ISO/IEC 27002:2013

Inventory of assets.

NIST 800-53 rev 4

Information system inventory.

CIS Critical Security Controls

Inventory of authorized and unauthorized devices.

CIS Critical Security Controls

The CIS rates Inventory of Authorized and Unauthorized Devices as the most important security control

The CIS Critical Security Controls (formerly the SANS Top Twenty) is a prioritized list of security controls developed by an international community of security professionals and institutions. The CIS rates Inventory of Authorized and Unauthorized Devices as the most important security control. This prioritization is designed to guide organizations to:

invest first in controls that will provide the greatest risk reduction and protection against the most dangerous threat actors and that can be feasibly implemented in your computing environment.

The phrase “can be feasibly implemented in your computing environment” deserves additional discussion because “feasibly implemented” does not translate to “easily implemented.” The control’s more detailed description:

Actively manage (inventory, track, and correct) all hardware devices on the network so that only authorized devices are given access and unauthorized and unmanaged devices are found and prevented from gaining access

offers insight about potential implementation challenges.

Managing devices by policy

Are you identifying unauthorized devices and preventing them from accessing your network?

The question of “What do you have?” has been expanded to “Are you identifying unauthorized devices and preventing them from accessing your network?” Preventing unauthorized device access starts with a policy, and organization management must buy into the policy and define any allowable exceptions. Otherwise, the policy will likely be undermined when influential people complain that they can’t connect their personal devices to the network.

Controlling which devices can connect to your network delivers benefits to both security and IT teams. From a security perspective, having only authorized devices on your network allows you to actively manage them to detect and remediate unauthorized software, misconfigurations, vulnerabilities and malware. Benefits also accrue to the IT organization. Having only authorized devices on the network increases network availability and eliminates the break-fix costs that inevitably result from troubleshooting problems often associated with one-off, unauthorized devices.

After the policy is established, automated supporting controls must be implemented to achieve the control objective.

More information

The CIS Critical Security Controls include six sub-controls that support Inventory of Authorized and Unauthorized Devices. A detailed discussion of these sub-controls is beyond the scope of this blog – but not to worry. Tenable is hosting a webinar on May 3rd, and we will dive into the details, show you how Tenable can help, and answer questions. This webinar is the first of a five-part series that will explore each of the CIS Foundational Cyber Hygiene controls. Brian Ventura, a SANS community instructor, will be our expert guest presenter. Brian teaches a 2-day course: Critical Security Controls: Planning, Implementing and Auditing. He has also taught a 5-day course: Implementing and Auditing the Critical Security Controls – in Depth. In addition to presenting valuable content, we will reserve time for questions and answers.

Look for future blogs where I will discuss the remaining Foundational Cyber Hygiene controls:

  • Inventory of authorized and unauthorized software
  • Secure configurations for hardware and software
  • Continuous vulnerability assessment and remediation
  • Controlled use of administrative privileges

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About Tenable
Tenable™, Inc. is the Cyber Exposure company. Over 24,000 organizations of all sizes around the globe rely on Tenable to manage and measure their modern attack surface to accurately understand and reduce cyber risk. As the creator of Nessus®, Tenable built its platform from the ground up to deeply understand assets, networks and vulnerabilities, extending this knowledge and expertise into™ to deliver the world’s first platform to provide live visibility into any asset on any computing platform. Tenable customers include over 50 percent of the Fortune 500, large government agencies and organizations across the private and public sectors. Learn more at
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