Definition

What is Defense in Depth?

A security strategy that layers multiple independent controls so that the failure of any single control does not result in a complete breach. The principle assumes no single technology or process is infallible, and combines preventive controls (firewalls, input validation), detective controls (SIEM, IDS), and corrective controls (incident response, backups) across people, processes, and technology. Defense in depth is a foundational concept in both network and application security architecture.

Related terms

Zero Trust →

A security model built on the principle that no user, device, or network segment should be implicitly trusted — even those already inside a traditional network perimeter.

Firewall →

A network security control that monitors and filters traffic between networks based on predefined security rules.

Web Application Firewall (WAF) →

A security control that monitors, filters, and blocks HTTP/HTTPS traffic between clients and a web application based on rule sets designed to detect common attack patterns.

Security Information and Event Management (SIEM) →

A platform that aggregates, normalizes, and correlates security event data from across an organization's infrastructure to support threat detection, incident investigation, and compliance reporting.

Put this into practice

AI penetration testing for web applications →

See how Penetrify's autonomous AI agents find and validate this class of security issue in your application.