Software Development Life Cycle (SDLC) Phases

What SDLC phases cover

software development life cycle phases are not just a project timeline, they are the control points where security expectations are set, verified, and enforced. For security teams, the value of the phase model is that it turns broad secure development goals into specific checkpoints for requirements, design, build, test, release, and operations.

Because each phase answers a different question, failures often happen when organisations treat SDLC as a linear handoff instead of a governance model. A requirement gap becomes a design flaw, a design gap becomes insecure code, and a release gap becomes an operational exposure.

Security controls across the phases

In the requirements phase, teams decide what security obligations the software must satisfy, including access control, logging, secrets handling, and trust boundaries. In the design phase, they define how those requirements are implemented, including authentication flows, privilege boundaries, dependency choices, and threat modeling. In the build and test phases, they verify whether the implementation matches the design and whether security defects are being introduced or missed.

In release and deployment, the focus shifts to whether the software can be shipped safely, with secure configuration, signed artifacts, controlled approvals, and dependable change governance. In operations and maintenance, the question becomes whether the running system still meets its security intent as code changes, dependencies change, and credentials, keys, or service accounts evolve.

Why SDLC phases matter for identity security

Identity controls are woven through the SDLC because software often depends on users, admins, service accounts, API keys, tokens, and deployment identities. If those identities are not considered early, teams tend to bolt on access control later, which usually creates privilege sprawl, weak secret handling, or brittle release processes.

The most common identity failure is phase mismatch: design assumes one trust model, implementation introduces another, and operations inherit the risk. That is why identity-aware SDLC practices must cover both human access and non-human access, especially where pipelines, production systems, and third-party services exchange credentials or signing material.

How to use the phase model in practice

Practitioners use SDLC phases to assign ownership and set security gates, not to create extra bureaucracy. A phase model works best when each stage has explicit entry and exit criteria, clear evidence requirements, and a defined owner for security decisions that cannot be deferred.

For teams building secure software, the useful habit is to ask at every phase what changed, what trust was introduced, and what must be rechecked before the next handoff. That keeps threat modeling, code review, testing, release approval, and operational monitoring connected to the same lifecycle instead of becoming isolated activities.

Risk and Threat Considerations

When SDLC phases are weakly defined or poorly enforced, security defects move downstream and become harder to detect, cheaper to exploit, and more expensive to fix. The biggest risk is not one bad phase, but the loss of continuity between phases, where a requirement, design, or release decision is never revalidated.

Failure mechanism: Attackers and internal failures both benefit when insecure defaults, leaked secrets, weak approvals, or missing tests survive from one phase into the next. In practice, that can create credential exposure, privilege abuse, insecure deployments, and defects that only surface after release.

Impact: The result can be compromised software, broken trust in releases, delayed remediation, and operational exposure that affects customers, administrators, and downstream systems.

Practitioner Guidance

Why practitioners should care: SDLC phase discipline is where security becomes repeatable. If the phase boundaries are vague, ownership drifts and security work gets rediscovered late, usually during incident response or urgent remediation.

Governance implication: Define which security checks belong in each phase and require proof that they happened before a release can advance. For teams that want a practical reference for secure development checkpoints, the Application Security Guide, the Secure Software Development Lifecycle (SSDLC) Guide, and the Secure SDLC Policy Template are useful navigation points for turning phase intent into operational controls.

Practitioner takeaway: Treat the SDLC as a control chain, not a documentation artifact, and make sure every phase leaves behind evidence that the next phase can trust.

Related resources from NHI Mgmt Group

• How do organisations implement System Development Life Cycle (SDLC)?
• Software Development Life Cycle
• System Development Life Cycle (SDLC)
• How should security teams implement secure software development policies across the SDLC?