The answer is the Design phase. Threat modeling is most effective during this stage of the secure SDLC because architectural decisions, data flow diagrams, trust boundaries, and component interactions are being defined, allowing security controls to be built into the system rather than bolted on later. This aligns with the ‘shift left’ principle, reducing cost and effort compared to retrofitting security after implementation. On the CISSP exam, this concept tests your understanding of the Software Development Security domain and the practical application of threat modeling as a proactive risk identification activity. A common trap is confusing the Design phase with the Requirements phase, but remember that requirements define what the system should do, while Design defines how it will be built—and threat modeling requires concrete architecture to analyze. A useful memory tip: “Design before you defend” or think of the mnemonic D.A.D. (Design, Analyze, Defend) to recall that threat modeling belongs in the Design phase.
CISSP Software Development Security Practice Question
This CISSP practice question tests your understanding of software development security. Read the scenario carefully and evaluate each option against the stated constraints before committing to an answer. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
A development team is adopting a secure SDLC. Which phase should include threat modeling to identify potential security vulnerabilities early?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Design
Threat modeling is a structured activity that identifies potential threats, vulnerabilities, and attack vectors against a system. It is most effective during the Design phase because architectural decisions, data flow diagrams, trust boundaries, and component interactions are being defined, allowing security controls to be built in rather than bolted on later. Performing threat modeling here aligns with the 'shift left' principle of secure SDLC, reducing cost and effort compared to retrofitting security after implementation.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
✗
Implementation
Why it's wrong here
Performing threat modeling during implementation is late; vulnerabilities identified may require costly rework.
✓
Design
Why this is correct
Threat modeling is a design-time activity that helps identify and address security threats before implementation.
Related concept
Read the scenario before looking for a memorised answer.
✗
Testing
Why it's wrong here
Testing is reactive; threat modeling should be proactive and occur earlier in the SDLC.
✗
Requirements gathering
Why it's wrong here
Threat modeling typically requires a design to analyze, so it is not usually performed during requirements gathering.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates confuse 'Requirements gathering' (where high-level security goals are set) with 'Design' (where concrete architectural decisions enable actionable threat modeling), leading them to pick D instead of B.
Detailed technical explanation
How to think about this question
Threat modeling methodologies like STRIDE (Spoofing, Tampering, Repudiation, Information Disclosure, Denial of Service, Elevation of Privilege) map directly to design elements such as data flow diagrams (DFDs) and trust boundaries. For example, a DFD revealing an unencrypted data flow across a network boundary would trigger a Tampering threat, prompting the design of TLS 1.3 or mTLS controls. In real-world scenarios, missing threat modeling at design time led to vulnerabilities like the 2017 Equifax breach, where an unpatched Apache Struts flaw was a design-level oversight in handling external inputs.
KKey Concepts to Remember
Read the scenario before looking for a memorised answer.
Find the constraint that changes the correct option.
Eliminate answers that are true in general but not in this case.
TExam Day Tips
→Watch for words such as best, first, most likely and least administrative effort.
→Review why wrong options are wrong, not only why the correct option is correct.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
How this comes up in practice
A security analyst at a medium-sized enterprise encounters this scenario during an investigation or architecture review. The correct answer reflects best practice for the specific threat or control described. Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option. Security exam questions test whether you can match controls to threats in context — not just recall definitions.
Related glossary terms
Concepts from this question explained
These glossary pages explain the core terms tested in this CISSP question in full detail.
Software Development Security — This question tests Software Development Security — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Design — Threat modeling is a structured activity that identifies potential threats, vulnerabilities, and attack vectors against a system. It is most effective during the Design phase because architectural decisions, data flow diagrams, trust boundaries, and component interactions are being defined, allowing security controls to be built in rather than bolted on later. Performing threat modeling here aligns with the 'shift left' principle of secure SDLC, reducing cost and effort compared to retrofitting security after implementation.
What should I do if I get this CISSP question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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Question Discussion
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