What principle means that all connections not explicitly allowed are automatically denied?

The principle that states all connections not explicitly allowed are automatically denied is known as "implicit deny." This concept is fundamental in security practices, serving as a foundational rule in network security and access control policies.

Implicit deny ensures that any traffic or connection that lacks a specific permission to pass through a firewall, router, or any security system is blocked by default. This approach minimizes potential vulnerabilities by preventing unauthorized access, as only predetermined and explicitly allowed traffic is granted entry.

By adopting an implicit deny strategy, organizations enhance their security posture by reducing the attack surface and mitigating risks associated with unintentional exposure of resources. This principle is essential for maintaining strict control over network traffic and ensuring that only trusted connections are permitted, thereby safeguarding sensitive information and system integrity.