In the software security development life cycle process, threat modeling occurs in which phase?

In Microsoft's SDL and most industry-standard SDLC frameworks, threat modeling takes place during the Design phase because it requires a system architecture or data-flow diagram to identify trust boundaries, entry points, and potential threats. Performing it at design time allows mitigations to be built into the architecture before any code is written, making remediation far less costly.

The Requirements phase focuses on gathering and documenting functional and security requirements, not on modeling specific threats against a defined architecture.

The Verification phase involves security testing, code review, and validation of controls already implemented, occurring after design and implementation.

The Implementation phase involves writing code; threat modeling should precede this phase so that developers have architectural guidance before building.