Web Security Fundamentals: Host-Only Cookies and Domain Scope

Every web application relies on cookies for session management, but misconfigured cookie domains can expose sensitive user data to subdomain hijacking. Understanding the subtle distinction between host-only cookies and domain-scoped cookies is critical for securing modern web platforms. This course provides a clear, text-based guide to managing cookie scope and security. You will transition from basic cookie usage to implementing precise domain restrictions, ensuring that your session identifiers and sensitive tokens remain strictly where they belong. What you'll learn: - Understand the core differences between host-only cookies and domain-scoped cookies - Configure the Domain directive correctly to control access across subdomains - Implement modern cookie attributes like Secure, HttpOnly, and SameSite for defense-in-depth - Analyze how modern browsers handle cookie partitioning and state restrictions - Practice identifying and fixing common cookie configuration vulnerabilities through written scenarios - Design secure-by-default cookie strategies for multi-tenant and single-domain applications The course begins with foundational concepts of HTTP state management before diving deep into cookie attributes, domain wildcard behaviors, and modern browser security policies. You will read through detailed architectural explanations and analyze real-world configuration examples to solidify your understanding. This course is designed for beginner web developers, security enthusiasts, and systems administrators who want to build a solid foundation in web application security. No prior security experience is required, though a basic familiarity with how HTTP requests work is helpful. Start reading today to secure your web applications against subdomain cookie leaks.