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Layered Defences: Building Blocks of Secure Organisations

Every organisation is different in terms of how it uses data, how its processes work, and how their staff conduct themselves. As a result no single security tool, deployment, implementation, or capability can protect them.

Layered defences, also known as “defence in depth,” is the approach of implementing multiple layers of security controls to protect against a wide range of threats, ensuring that if one layer fails, others are in place to mitigate the risk. Furthermore, each layer is designed to address specific types of threats, creating a comprehensive shield that protects against potential attacks.

The concept of layered defences is ancient. Our most striking example comes from a time before the computer, when threats would manifest themselves physically against nation-states – castles are the key epitome of a layered defence. The combination of moats, drawbridges, walls, battlements, keeps, towers, turrets, guards, and gatehouses provided a multi-layered defence system that not only protected the castle, but also its inhabitants.

 Regardless of if we are talking about fortifications, or digital estates, by diversifying defences across various points of vulnerability, organisations can reduce the likelihood of a successful breach and limit the impact of security incidents.

The Core Layers of Cybersecurity Defence

To build an effective layered defence strategy, organisations must consider various aspects of their IT environment and implement appropriate security measures at each level. Below are the core layers typically involved in a robust cybersecurity defence:

Perimeter Security

Perimeter security is the first line of defence, focusing on preventing unauthorized access to the network. Common controls at this layer include firewalls which support domain reputation services, intrusion detection and prevention systems (IDPS), secure gateways, mail filters, and intercepting SSL/TLS inspecting proxies. These tools help monitor and filter traffic, blocking malicious activity before it reaches the internal network.

Network Security

Once traffic passes through the perimeter, network security controls come into play. These measures include network segmentation, virtual private networks (VPNs), and network access control (NAC). Network security ensures that even if an adversary gains access to the perimeter, they are limited in their ability to move laterally within the network.

Endpoint Security

With the proliferation of remote work and mobile devices, securing endpoints has become increasingly important. Endpoint security involves installing antivirus software, endpoint detection and response (EDR) tools, and ensuring that devices are patched and up to date. This layer helps protect individual devices from being compromised and becoming entry points for adversaries.

Application Security

Adversaries often target applications due to their complexity and potential vulnerabilities. Application security focuses on securing software applications through secure coding practices, regular updates, and the use of web application firewalls (WAFs). By protecting applications, organisations can prevent attacks such as SQL injection, cross-site scripting (XSS), and other common exploits which may result in an adversary gaining an additional foothold or obtaining material which could further ran attack.

Data Security

At the heart of every cybersecurity strategy is the protection of data. Data security measures include encryption, data loss prevention (DLP) tools, and access controls that ensure only authorised users can access sensitive information. By securing data both at rest and in transit, organisations can reduce the risk of data breaches and ensure compliance with regulations.

Identity and Access Management (IAM)

IAM is crucial for ensuring that only the right individuals have access to the right resources at the right time. Implementing strong authentication methods, such as multi-factor authentication (MFA), and managing user privileges through role-based access control (RBAC) are essential components of IAM. This layer helps prevent unauthorised access and reduces the risk of insider threats, and limits an adversaries ability to make rapid progress should they manage to compromise an endpoint and its user.

Security Awareness and Training

The human element is often the weakest and the strongest link in cybersecurity. Providing regular security awareness training and promoting a security-conscious culture are vital components of a layered defence strategy. Educating employees on phishing, social engineering, and safe online practices can significantly reduce the likelihood of human error leading to a security incident. Furthermore, motivated and supported staff are more willing and likely to report unusual behaviour which could be indicative of an ongoing threat. Giving staff the tools to effectively report, and regularly praising, listening to feedback, and rewarding behaviours that protect the organisation benefits the whole business. Businesses which dictate security, punish one-off breaches, and have a culture which derides or ridicules staff who have fallen victim to an adversary, will often suffer more in the long term as staff become more fearful to report incidents as it could harm their career.

Incident Response and Recovery

Despite the best defences, breaches can and will still occur – no organisation will achieve 100% security and stay in business. Having a robust incident response and recovery plan is essential for minimising the impact of a security incident. This layer includes incident detection, response planning, regular drills, and data backups. Being prepared to respond quickly and effectively can make all the difference in mitigating damage and restoring normal operations.

The Benefits of a Layered Defence Approach

• Redundancy and Resilience: A single security control can be bypassed or fail, but multiple layers ensure that an attack must overcome several hurdles, increasing the chances of detection and prevention.
• Comprehensive Protection: Different layers address different types of threats, ensuring that the organisation is protected from various angles. This multi-faceted approach is more effective than relying on a single line of defence.
• Reduced Attack Surface: By implementing security measures at various points, organisations can minimize their attack surface, making it more difficult for adversaries to find vulnerabilities.
• Improved Incident Response: Layered defences provide multiple opportunities to detect and respond to threats, allowing for quicker identification and mitigation of attacks.

Trust and Verify

Implementing these defences is only one part of the story. They need to be regularly exercised and maintained. This is where  vulnerability scans can identify missing patches, misconfigured ports, and exposed appliances; penetration tests can evaluate individual layers; purple teaming can enhance the detection capabilities; and red teams can examine end-to-end attack paths, exercising as many of the layers as possible to identify gaps, and exercise incident responses. This can occur in both digital, and physical environments of the organisation. Through conducting these tests we can verify that they are not drifting, and this in turn acts as an additional layer of defence.

Conclusion

A  layered defence strategy is not just an option—it is a necessity. By implementing multiple layers of security controls and assessing them, organisations can better protect their assets, reduce the risk of successful attacks, and ensure a more resilient cybersecurity posture.

Investing in layered defences means thinking holistically about security, considering all potential vulnerabilities, and preparing for the unexpected. In the long run, this approach will not only safeguard your organisation’s digital assets but also build trust with customers, partners, and stakeholders who rely on your commitment to security.