Non-Functional Requirements (NFRs) Framework for Software Systems

Overview

Security Non-Functional Requirements (NFRs) define how a software system must protect identities, access, data, secrets, configurations, code, infrastructure, integrations, and operational activity from unauthorized use, compromise, misuse, disclosure, disruption, and attack. Security requirements should be explicit because they influence architecture, design, development, testing, deployment, operations, monitoring, incident response, compliance, and audit readiness.

Security NFRs should define the expected protection level, applicable controls, validation method, evidence source, owner, and approval expectations. They should also account for users, administrators, service accounts, non-human identities, interfaces, APIs, cloud services, third-party dependencies, logs, privileged workflows, and production operations.

Best Practice: Define authentication non-functional requirements

Description

Authentication NFRs define how users, administrators, services, integrations, workloads, and non-human identities prove their identities before accessing the system. They should specify supported identity providers, authentication factors, token requirements, session controls, service-to-service identity, privileged access requirements, and authentication failure handling.

Benefits

Authentication requirements reduce the risk of unauthorized access, credential misuse, weak identity proofing, uncontrolled service accounts, and inconsistent access behavior across environments and integrations.

Example non-functional requirements

• The software system shall authenticate all interactive users through the approved enterprise identity provider before granting access to protected application functions.

• Validation method: Validate through identity-provider integration testing, access testing with valid and invalid accounts, and review of authentication configuration in each target environment.

• Example validation evidence: Authentication test report, identity provider configuration export, access test results, login audit logs, and security review approval.

• All service-to-service calls shall use approved non-human identity mechanisms and shall not rely on shared static user credentials.

• Validation method: Validate through configuration inspection, code review, secrets scan, and integration testing that verifies service identity and token use.

• Example validation evidence: Service identity configuration, code review record, secrets scan report, integration test logs, and architecture/security approval.

Related stakeholders

Typical stakeholders include security architects, identity and access management teams, application architects, developers, platform engineers, QA teams, operations teams, compliance stakeholders, and audit stakeholders.

Related lifecycle phases

Authentication NFRs are defined during requirements, architecture, and design; implemented during development and platform configuration; validated during integration testing, security testing, release readiness, operational monitoring, and periodic access review.

Best Practice: Define authorization and access-control non-functional requirements

Description

Authorization and access-control NFRs define what authenticated users, roles, groups, services, administrators, tenants, and automated processes are allowed to view, create, change, approve, execute, export, delete, or administer. These requirements should include least privilege, segregation of duties, privileged access, administrative controls, role mapping, policy enforcement, and access review expectations.

Benefits

Authorization requirements prevent excessive access, unauthorized transactions, tenant data leakage, inappropriate administrative action, and uncontrolled privilege escalation. They also support privacy, compliance, audit, and operational accountability.

Example non-functional requirements

• The software system shall enforce role-based access control for all protected user functions, including view, create, update, approve, export, delete, and administrative actions.

• Validation method: Validate through positive and negative access-control tests for each role and protected function, including attempts to bypass the user interface through direct API calls.

• Example validation evidence: Access-control test matrix, API authorization test results, role-to-permission mapping, defect records, and security approval.

• Administrative access shall require privileged role assignment, approval, logging, and periodic review.

• Validation method: Validate through privileged access review, administrative workflow testing, log inspection, and review of approval records.

• Example validation evidence: Privileged access approval records, access review evidence, administrative action logs, and audit signoff.

Related stakeholders

Typical stakeholders include product owners, business process owners, security architects, IAM teams, compliance teams, application architects, developers, QA teams, and audit stakeholders.

Related lifecycle phases

Authorization NFRs are defined during requirements, business process design, architecture, and security design; validated during development, integration testing, security testing, UAT, release readiness, access recertification, and audit review.

Best Practice: Define encryption non-functional requirements

Description

Encryption NFRs define how data, secrets, credentials, tokens, messages, files, backups, logs, and communications are protected from unauthorized disclosure or tampering while stored, transmitted, processed, or retained. They should identify encryption scope, approved algorithms, key management expectations, certificate requirements, rotation rules, and exception handling.

Benefits

Encryption requirements reduce exposure from data theft, network interception, lost media, compromised backups, weak configuration, and unauthorized access to stored or transmitted information.

Example non-functional requirements

• All sensitive data stored by the system shall be encrypted at rest using approved enterprise encryption standards and managed keys.

• Validation method: Validate through database, storage, backup, and cloud configuration review and confirm that sensitive data stores use approved encryption settings and key ownership.

• Example validation evidence: Configuration evidence, key management record, storage encryption report, backup encryption evidence, and security architecture approval.

• All external and internal API traffic containing protected data shall use approved transport encryption and reject unsupported protocol versions and weak cipher suites.

• Validation method: Validate through TLS configuration scanning, API integration testing, and network security review.

• Example validation evidence: TLS scan results, API test logs, gateway configuration, certificate inventory, and security test report.

Related stakeholders

Typical stakeholders include security architects, platform engineers, infrastructure teams, cloud teams, database administrators, developers, QA teams, privacy stakeholders, and compliance stakeholders.

Related lifecycle phases

Encryption NFRs are defined during architecture, security design, data design, and platform design; validated during configuration review, security testing, integration testing, release readiness, and recurring control review.

Best Practice: Define secrets management non-functional requirements

Description

Secrets management NFRs define how credentials, keys, certificates, tokens, passwords, connection strings, signing keys, and other sensitive secrets are created, stored, accessed, rotated, revoked, monitored, and protected. They should prohibit secrets in source code, configuration files, logs, images, and unmanaged locations.

Benefits

Secrets management requirements reduce the risk of credential leakage, unauthorized system access, weak rotation practices, accidental exposure in repositories or logs, and unmanaged operational access.

Example non-functional requirements

• All application secrets shall be stored in an approved secrets management service and shall not be stored in source code, build artifacts, container images, application logs, or plain-text configuration files.

• Validation method: Validate through secrets scanning, repository review, container image scanning, configuration inspection, and runtime configuration review.

• Example validation evidence: Secrets scan report, repository review results, container scan report, configuration review record, and security approval.

• Secrets used by production workloads shall have documented ownership, access policy, rotation expectation, and revocation procedure.

• Validation method: Validate through secrets inventory review, access-policy inspection, rotation evidence review, and operations runbook review.

• Example validation evidence: Secrets inventory, access policy export, rotation logs, revocation runbook, and operations/security signoff.

Related stakeholders

Typical stakeholders include security teams, developers, DevOps teams, platform engineers, cloud teams, operations teams, and audit stakeholders.

Related lifecycle phases

Secrets management NFRs are defined during architecture, development standards, CI/CD design, and operations design; validated during code review, pipeline scanning, deployment review, release readiness, and recurring security control review.

Best Practice: Define vulnerability management non-functional requirements

Description

Vulnerability management NFRs define how security weaknesses are identified, classified, prioritized, remediated, retested, excepted, monitored, and reported across applications, infrastructure, dependencies, containers, APIs, configuration, and cloud services. They should specify severity thresholds, remediation timelines, exception approvals, and evidence expectations.

Benefits

Vulnerability management requirements make security risk visible and actionable. They help prevent known weaknesses from accumulating in production systems and create a governance path when remediation cannot happen immediately.

Example non-functional requirements

• Critical and high vulnerabilities affecting production components shall be remediated or formally risk-accepted within approved severity-based remediation timelines.

• Validation method: Validate by reviewing vulnerability scan results, remediation records, retest results, and risk acceptance approvals against the approved remediation policy.

• Example validation evidence: Vulnerability dashboard, remediation tickets, retest evidence, exception approvals, and security governance report.

• The system shall run vulnerability scanning for application code, dependencies, containers, and infrastructure configuration before production release.

• Validation method: Validate through pipeline evidence showing completed scans, resolved blocking findings, and approved exceptions before release approval.

• Example validation evidence: Pipeline scan results, release approval checklist, resolved defect records, exception register, and security signoff.

Related stakeholders

Typical stakeholders include security operations, application security, developers, platform teams, product owners, release managers, compliance teams, and risk stakeholders.

Related lifecycle phases

Vulnerability management NFRs are defined during security planning and release governance; validated during development, CI/CD execution, security testing, release readiness, production monitoring, and recurring vulnerability review.

Best Practice: Define secure coding non-functional requirements

Description

Secure coding NFRs define how application code must be designed, written, reviewed, scanned, and maintained to reduce common software weaknesses. They should address input validation, output encoding, session management, error handling, dependency use, secure defaults, logging safety, injection prevention, and peer review expectations.

Benefits

Secure coding requirements reduce preventable vulnerabilities, improve code quality, improve maintainability, and support repeatable software assurance across delivery teams and AI-assisted coding workflows.

Example non-functional requirements

• All externally supplied input shall be validated using approved server-side validation rules before being used in business logic, queries, commands, or downstream integrations.

• Validation method: Validate through code review, static analysis, unit tests, API tests, and negative testing for invalid, malformed, oversized, and malicious inputs.

• Example validation evidence: Code review record, static analysis report, unit test results, negative API test results, and defect remediation evidence.

• Application error handling shall not expose stack traces, secrets, protected data, internal paths, or infrastructure details to end users or external callers.

• Validation method: Validate through error-condition testing, API response review, log review, and security testing that simulates common exception conditions.

• Example validation evidence: Error-handling test report, API response samples, log samples, security test results, and release approval evidence.

Related stakeholders

Typical stakeholders include developers, application architects, security architects, QA teams, code reviewers, DevSecOps teams, and engineering managers.

Related lifecycle phases

Secure coding NFRs are defined during development standards and solution design; implemented during coding; validated during peer review, static analysis, unit testing, integration testing, security testing, and release readiness.

Best Practice: Define security testing and penetration testing non-functional requirements

Description

Security testing and penetration testing NFRs define what types of security validation must be performed, when they must occur, which systems and interfaces are in scope, what severity thresholds block release, and what evidence is required. Testing may include static analysis, dynamic analysis, software composition analysis, API testing, cloud configuration review, threat simulation, red-team testing, and penetration testing.

Benefits

Security testing requirements give teams a consistent way to prove that security controls are working and that known weaknesses have been found, remediated, or approved as risk exceptions before production use.

Example non-functional requirements

• The system shall complete security testing for all externally exposed APIs before production release, including authentication, authorization, input validation, error handling, and rate-limit behavior.

• Validation method: Validate through API security test execution, penetration test sampling, and review of resolved or accepted findings before release approval.

• Example validation evidence: API security test report, penetration test summary, remediation tickets, risk acceptance records, and release security signoff.

• No unresolved critical or high penetration test findings shall remain open at production release unless formally risk-accepted by authorized security and business stakeholders.

• Validation method: Validate through release readiness review comparing penetration test findings, remediation status, retest results, and exception approvals.

• Example validation evidence: Penetration test report, remediation evidence, retest report, exception approval, and release readiness checklist.

Related stakeholders

Typical stakeholders include application security teams, penetration testers, developers, QA teams, architects, product owners, release managers, risk stakeholders, and compliance stakeholders.

Related lifecycle phases

Security testing NFRs are defined during test planning and release governance; validated during development, integration testing, pre-production testing, release readiness, post-release testing, and recurring control review.

Best Practice: Define security validation and evidence non-functional requirements

Description

Security validation and evidence NFRs define the proof required to show that security requirements and controls have been implemented and are operating as expected. Evidence may include test reports, scan results, configuration exports, approval records, threat model reviews, access review records, audit logs, and monitoring data.

Benefits

Security validation evidence makes security requirements auditable and governable. It prevents teams from relying only on security intent, architecture assumptions, or unverified tool output.

Example non-functional requirements

• Each critical security NFR shall identify a validation method, evidence source, validation owner, and approval stakeholder before production release.

• Validation method: Validate through requirements traceability review and release readiness review to confirm that every critical security NFR has required validation metadata and completed evidence.

• Example validation evidence: Security NFR traceability matrix, validation plan, evidence repository links, release checklist, and approval record.

• Security validation evidence shall be retained for each production release and made available for risk, compliance, audit, and incident review.

• Validation method: Validate by sampling release records and confirming that required security evidence exists, is accessible, and maps to approved security NFRs.

• Example validation evidence: Release evidence repository, security test reports, scan results, approval records, audit sampling evidence, and retention evidence.

Related stakeholders

Typical stakeholders include security teams, architects, QA teams, release managers, compliance stakeholders, audit stakeholders, product owners, and risk stakeholders.

Related lifecycle phases

Security validation and evidence NFRs are defined during requirements, security planning, and release governance; validated during test execution, release readiness, recurring control review, audit review, and post-incident review.