Secure Software Development Lifecycle (SDLC) is a software development model that adds security controls at every stage of building an application, from planning and design to coding, testing, release, and maintenance. Instead of treating security as a final review, teams use secure requirements, threat modeling, code review, dependency scanning, testing, and release checks throughout the process.
This matters because many attacks exploit weaknesses that were introduced early and discovered late. If security is built into the SDLC, teams can catch insecure design choices, vulnerable libraries, and implementation flaws before they reach production. In defense, SDLC practices help reduce backlog, speed up remediation, and prevent the same weakness from recurring. In real incidents, a weak SDLC often shows up as unvalidated input handling, exposed secrets, missed patching, or rushed releases with incomplete testing.