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What is Defense in Depth?

What is Defense in Depth?

Harold Bell
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Key Takeaways

Defense in Depth (DiD) is a cybersecurity strategy that involves deploying multiple defensive layers. DiD employs physical, technical, and administrative controls to create robust barriers against cyber threats. Incorporating principles like least-privilege access and behavioral monitoring, DiD aims to thwart attackers by increasing the number of obstacles they must overcome.

Defense in Depth (DiD) is a cybersecurity strategy that involves deploying multiple types of defensive layers. The underlying theory holds that digital assets will be better protected if a malicious actor has to penetrate more than one barrier to succeed in an attack. This article explores how DiD works.

What is Defense in Depth?

The cybersecurity profession borrowed the concept of DiD from the military, which has historically created multiple physical perimeters around a target. A medieval castle, for example, had a moat, high stone walls, special windows designed for shooting arrows, and walkways atop the walls where defenders could pour boiling water on anyone climbing up the walls. The moat, the walls, the arrows—each was part of a defense-in-depth strategy. On their own, they might not work well, but collectively, they created a strong defensive barrier.

So it is in cybersecurity, give or take. An attack target, like a database, has a depth of defenses that include physical barriers against manipulation of hardware, network access controls, passwords, and threat detection systems. These are the equivalent of a military’s concentric perimeters. As a whole, these countermeasures create better security than they would on a standalone basis. That’s DiD.

How does Defense in Depth work?

There is no single, standardized way to implement DiD. It’s dynamic, changing as newer methods arise and workload requirements change. Different workloads and organizational security priorities will dictate how a security team will set up its DiD architecture. In general, though, DiD usually works through a combination of the following types of controls:

  • Physical — In this era of cloud computing, it’s easy to forget that hardware, including servers, storage arrays, network switches and the like, is vulnerable to physical interference. With physical access to a server, for example, an attacker could install a root kit on the spot and hijack the machine. To prevent this from occurring, data centers employ physical controls like biometric scanners, alarms, video surveillance, and so forth.
  • Technical — These include software- and hardware-based controls that mitigate network-borne threats like distributed denial of service (DDoS) attacks, malware, phishing, and ransomware. Technologies like firewalls, secure web gateways (SWGs), and extended detection and response (XDR) solutions help realize the technical controls that migrate threats coming over the network.
  • Administrative — This is the arena of security policy. Administrative controls include identity and access management (IAM) and password rules. If you’re managing an AWS environment for example, this would be your responsibility according to the Shared Responsibility Model. This model ironically is a great example of a DiD strategy.

What are the elements of Defense in Depth?

DiD takes shape as security managers apply the controls outlined above according to the dominant principles of cybersecurity. These are the core elements of DiD:

  • Least-privilege access — Setting a policy that a user should only have the fewest possible privileges is a way to execute a defense-in-depth strategy. This way, if a malicious actor gains access to the network, his ability to breach sensitive data or disrupt operations will be limited.
  • Secure development and supply chain — Software must be subject to security controls as it makes its way from development through testing and into production. This practice ensures that new software will not introduce vulnerabilities. The software supply chain must also be similarly secured. Blocking an attacker’s path through software adds a tier of defense in a DiD architecture.
  • Network segmentation — Separating sensitive applications and data onto different network segments is an effective way to bar malicious actors from “lateral movement” across a network. This practice acts like the castle walls. If an attacker crosses the moat, he still has to scale the wall.
  • Behavioral monitoring and analysis — Even with multiple tiers of countermeasures, attackers can still get through. Insiders also pose a threat. To mitigate this risk, it is necessary to engage in constant monitoring and analysis of user and system behavior. This process can identify anomalous events that could suggest an attack is underway.
  • Zero trust — With its foundational rule of “never trust, always verify,” Zero Trust prevents much unauthorized access. It adds to the effectiveness of a DiD architecture.
  • Resiliency — The ability to restore IT operations is another tier of DiD. With strong backup and restore functions in place, an organization can recover from even a serious cyber incident, such as a ransomware attack.

What is layered security?

Some people describe DiD as “layered security,” but while each area of DiD protection might be referred to as a layer, the term ‘layered security’ means something different in cybersecurity circles. Layered security refers to deploying multiple security tools to address a single area of security. For example, a firewall and an intrusion prevention system (IPS) both block unwanted access, but they achieve this goal in different ways. Each is a layer of security that works against network penetration.

How does layered security differ from integrated security?

Integrated security is an approach to cybersecurity that relies on connecting multiple security tools to achieve more effective overall threat detection and response. An integrated security model could complement a layered security architecture, connecting different layers into a coherent stack.

For example, firewalls and antivirus software can be integrated with a security incident and event management (SIEM) solution. The SIEM ingests and analyzes data from the firewall and antivirus software to detect threats that neither tool saw on its own. The SIEM may also be integrated with incident response platforms, such as security automation, orchestration, and response (SOAR)—enabling better responses to attacks than are not possible with piecemeal or overly manual processes.


DiD, layered security, and integrated security should not be isolated security strategies. Rather, it is optimal if they are designed to work together. DiD may comprise a layered security architecture, with different layers integrated with one another for more powerful security capabilities overall. The underlying principles remain the same, no matter how the security architecture is set up: The more countermeasures standing between the target and the attacker, the more likely it will be that the attacker fails. That’s the enduring objective of defense in depth.

Defense in Depth FAQs

What are the advantages of defense in depth?

Defense in depth (DiD) provides several advantages for businesses. It enhances resilience by diversifying security measures, ensuring that if one layer is breached, others remain intact. Additionally, DiD improves detection capabilities by increasing visibility across the environment, enabling timely identification of suspicious activities.

Defense in depth aligns with regulatory and compliance requirements, such as GDPR and PCI DSS, by implementing robust security controls. Adhering to these standards mitigates legal and financial risks and fosters trust among customers and stakeholders. Overall, defense in depth offers a comprehensive and effective approach to security.

How can I implement defense in depth in my organization?

To implement a defense in depth strategy in your organization, you must follow a structured approach that encompasses several key steps:

  1. Assess risks: Begin by conducting a thorough risk assessment to identify potential security threats and vulnerabilities to your organization, including data breaches, API security threats, malware infections, or insider threats.
  2. Develop a security policy: Develop a security policy that outlines the organization’s security objectives, standards, and procedures.
  3. Implement security controls: Deploy a range of security controls across multiple layers of your organization’s IT infrastructure.
  4. Regularly update and test: Regularly update and patch software, firmware, and security systems to address known vulnerabilities and protect against emerging threats.
  5. Educate employees: Provide comprehensive security awareness training about common security risks, best practices, and procedures.
  6. Monitor and adapt: Implement continuous monitoring tools and processes to monitor network traffic, system logs, and user activities for signs of suspicious behavior or security incidents.

How does defense in depth relate to other cybersecurity strategies?

DiD is a cybersecurity strategy that involves deploying several layers of defense mechanisms to protect against various threats and vulnerabilities. However, defense in depth is often complemented by other cybersecurity strategies. One such strategy is Zero Trust, which focuses on verifying every user and device that attempts to access resources, regardless of their location or network perimeter.

Noname Security offers advanced security solutions, including API security testing tools and runtime protection, that can help organizations implement DiD and Zero-Trust strategies. You can request a demo to explore how we ensure robust protection against a wide range of threats and vulnerabilities.

How often should defense in depth measures be reviewed and updated?

Defense in depth measures should be reviewed and updated regularly to adapt to evolving threats and changes in the organization’s environment. As cybersecurity threats evolve, organizations must stay proactive in maintaining their defenses. Regular security testing, assessments, and audits ensure that security controls remain effective and aligned with the organization’s risk profile.

Harold Bell

Harold Bell was the Director of Content Marketing at Noname Security. He has over a decade of experience in the IT industry with leading organizations such as Cisco, Nutanix, and Rubrik, and has been featured as an executive ghostwriter in Forbes Technology Council and Hacker News.

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