Secure Software Development Lifecycle: Embedding Security into Every Sprint

The average cost of a data breach in 2025 exceeds $4.5 million. The majority of successful attacks exploit known vulnerability categories—SQL injection, XSS, broken authentication—that are entirely preventable with disciplined secure development practices.

Phase 1: Security Requirements

Security requirements must be defined alongside functional requirements, not after. For every feature, ask: What data does this handle? Who can access it? What are the abuse cases?

Use threat modelling (STRIDE or Attack Trees) to systematically identify security risks before a line of code is written. The earlier a threat is identified, the cheaper it is to mitigate.

Phase 2: Secure Design

Security architecture principles:

• Defence in depth: Multiple layers of controls, not reliance on any single mechanism
• Least privilege: Components and users access only what they need
• Fail secure: On error, default to denying access, not granting it
• Separation of duties: No single component or person can compromise the system alone

Phase 3: Secure Coding

Input validation: Validate and sanitise all inputs at the boundary. Reject anything that doesn't match the expected schema.

Parameterised queries: SQL injection is 30 years old and entirely preventable. Use ORM or parameterised queries—never string concatenation in SQL.

Output encoding: Encode all user-controlled data before rendering in HTML, JavaScript, or CSS contexts.

Secrets management: No secrets in code, ever. Use environment variables injected at runtime from a secrets manager.

Phase 4: Security Testing

• SAST (Static Application Security Testing): Analyse code for vulnerabilities in CI/CD
• DAST (Dynamic Application Security Testing): Test running applications for vulnerabilities
• Dependency scanning: Check for known CVEs in libraries (Snyk, Dependabot)
• Annual penetration testing by qualified external testers

Phase 5: Secure Deployment and Operations

Harden infrastructure, enable WAF, monitor for anomalous behaviour, maintain an incident response plan, and patch promptly when vulnerabilities are disclosed.