What Is Security by Design?
Security by Design builds security into systems from the start rather than adding it later.
Security by Design Principles
Minimize Attack Surface
Every feature, protocol, open port, service, and user interface is potential attack surface. Security by design minimizes attack surface by removing or disabling everything that is not required for the system's intended function. A system that exposes only the minimum necessary functionality has fewer opportunities for exploitation than a system that includes every available feature by default.
Principle of Least Privilege
Every user, service, and component should have the minimum permissions necessary to perform its function. A system designed on least privilege principles builds access controls that scope each role to exactly what it needs, rejects requests that exceed that scope, and provides no pathway to privilege escalation within the system itself.
Defense in Depth
Security by design assumes that individual controls will fail and layers multiple independent controls so that no single failure creates complete vulnerability. Authentication fails; rate limiting provides a second layer. Input validation fails; parameterized queries prevent SQL injection at the database layer. Encryption fails; data classification limits what data is exposed. Each layer provides independent protection that reduces the impact of other controls failing.
Secure Defaults
Security by design ships systems in a secure configuration by default, requiring explicit action to reduce security. Most enterprise software has historically shipped with insecure defaults — enabling all features, using weak default credentials, disabling encryption for performance. CISA's Secure by Design initiative advocates for shifting this model: requiring vendors to ship secure defaults and make insecurity opt-in rather than the default state.
Secure by Design in Practice
CISA's Secure by Design initiative, launched in 2023 and expanded in 2024, has produced a significant shift in how major software vendors think about security defaults. The initiative has encouraged vendors to adopt default MFA, eliminate default passwords, provide secure logging enabled by default, and reduce entire vulnerability classes through architectural decisions rather than patch-based remediation.
Security by Design in Acquisition Assessment
For PE sponsors evaluating software companies, Security by Design practices are indicators of engineering culture that affect long-term technical risk. A software company whose products ship with insecure defaults, require significant customer configuration to be secure, and accumulate security vulnerabilities at high rates reflects an engineering culture that has not internalized security as a design requirement. This has implications for both the company's own security posture and its customer relationships as enterprise buyers increasingly require evidence of secure development practices.
Related Reading
What is Security by Design?
Security by Design is the principle that cybersecurity should be built into systems, software, and infrastructure from the earliest stages of design and architecture rather than added as an afterthought. It encompasses architectural decisions, development practices, and default configurations that make systems secure in their baseline state, requiring explicit effort to make them less secure. CISA's Secure by Design initiative, launched in 2023, has driven industry-wide adoption with over 200 major software vendors pledging measurable security improvements.
What are the core principles of Security by Design?
Minimize attack surface (remove or disable everything not required for intended function), principle of least privilege (every user and component has minimum permissions needed), defense in depth (layer multiple independent controls so single failures don't create complete vulnerability), and secure defaults (ship systems in secure configuration requiring explicit action to reduce security). These principles produce systems where security is the default state rather than an opt-in feature requiring customer configuration.
How is Security by Design different from secure software development lifecycle (SDLC)?
Secure SDLC integrates security activities — threat modeling, code review, security testing, vulnerability scanning — into the development process. Security by Design is broader and more architectural: it addresses the fundamental design decisions that determine what classes of vulnerabilities are possible. SDLC catches vulnerabilities in code; Security by Design eliminates the vulnerability classes through architectural choices. A memory-safe language eliminates buffer overflow vulnerabilities by design; SDLC scanning catches buffer overflows in unsafe code. Both are valuable; Security by Design is more impactful because it prevents rather than detects.
What is the CISA Secure by Design pledge?
CISA's Secure by Design pledge, launched in 2023, has been signed by over 200 major software vendors including Microsoft, Google, Amazon, IBM, Palo Alto Networks, and others. Signatories commit to measurable security improvements within one year: increasing MFA adoption across products, eliminating default passwords, reducing entire classes of vulnerabilities through architectural change, enabling security logging by default, and increasing transparency through security advisories and vulnerability disclosure. The pledge represents a structural shift from reactive patching to proactive design.
Which programming languages and frameworks support Security by Design?
Memory-safe languages — Rust, Go, Swift, Kotlin, C#, Java, Python — eliminate entire vulnerability classes (buffer overflows, use-after-free, double-free) by design. CISA has explicitly advocated for migration away from C and C++ for new development. Frameworks that provide secure defaults — parameterized query interfaces, automatic output encoding, built-in authentication libraries, secure session management — reduce the surface area for developer error. Cloud-native architectures with managed identity, automatic encryption, and policy-as-code enable Security by Design at the infrastructure layer.
How should buyers evaluate vendor Security by Design practices?
Evaluate whether the vendor signed the CISA Secure by Design pledge and has published measurable progress; whether products ship with secure defaults (MFA enabled, no default passwords, logging enabled) requiring customers to opt out rather than opt in; whether the vendor publishes a clear vulnerability disclosure policy and security advisory program; and whether security architecture documentation describes how vulnerability classes are eliminated rather than just how vulnerabilities are patched. For software acquisition due diligence, these indicators reflect long-term engineering culture and technical risk.
What is the most important Security by Design improvement most organizations should make?
Eliminate default credentials and require strong authentication at first use for any product or system. Default passwords and disabled MFA produce immediate exploitable conditions that exist before any other security control activates. CISA's analysis of common attack patterns consistently identifies default credentials as one of the most exploited initial access vectors. For organizations building software, ship with MFA required by default. For organizations buying software, refuse to deploy products that ship with default credentials or that make MFA opt-in rather than required.
Real-World Example: CISA Secure by Design Pledge — Industry Response
CISA's Secure by Design pledge, launched in 2023, has been signed by over 200 major software vendors including Microsoft, Google, Amazon, IBM, and Palo Alto Networks. Signatories commit to measurable security improvements within one year: increasing MFA adoption across products, reducing entire classes of vulnerabilities, and increasing transparency through security advisories. The pledge represents a structural shift in how the software industry approaches security — from reactive patching to proactive design. Organizations evaluating software vendors can use pledge participation and progress as an indicator of security design culture.
Of software vulnerabilities could be eliminated by adopting Secure by Design architectural principles rather than patching individual vulnerabilities as they are discovered — per CISA analysis of common vulnerability root causes.