Quality by Design is a planning approach that builds quality into a process or system from the outset instead of trying to inspect it in later. In cyber security, that means designing software, infrastructure, and operations so that security requirements, testing, and controls are part of the architecture from day one. Examples include threat modeling, secure defaults, least privilege, code review, and automated validation.
This matters because many security failures come from design decisions made too late to fix cheaply. If authentication, logging, input handling, or segmentation are bolted on after deployment, gaps often remain. Quality by Design supports defense by making those controls explicit early, while attackers often benefit when teams rely on patching, manual checks, or inconsistent configurations. In practice, it shows up in secure development lifecycles, infrastructure-as-code reviews, and systems built to be verifiable, resilient, and harder to misuse.