DRY means “Don’t Repeat Yourself.” It is a design rule that says each important piece of logic, policy, or data definition should exist in one authoritative place, rather than being copied into multiple files, functions, or services. When the same behavior is duplicated, future changes can become inconsistent: one copy is updated while another is forgotten.
In cyber security, DRY matters because inconsistency creates security gaps. Repeated access checks, validation rules, or configuration values can drift and leave one code path weaker than another. Attackers look for these mismatches to bypass controls, trigger unexpected behavior, or exploit outdated logic. Defenders use DRY to centralize security decisions, reduce maintenance errors, and make audits easier. A DRY codebase is usually simpler to review, patch, and harden because there are fewer hidden versions of the same rule to miss.