27.3: ISO 27001 and Supply Chain Requirements¶

ISO 27001 has served as the international gold standard for information security management systems for two decades. The 2022 revision significantly strengthened supply chain security requirements, reflecting the growing recognition that organizational security depends fundamentally on the security of suppliers and service providers. For organizations operating internationally or serving enterprise customers, ISO 27001 certification often represents a baseline expectation—and the updated supplier relationship controls mean that certification now requires demonstrable supply chain security capability.

The urgency behind the 2022 revision's supplier controls is evident in breach statistics: research indicates that 53% of breaches now originate through suppliers, even as only 43% of companies systematically monitor third parties. This gap—between where attacks occur and where defenses focus—motivated ISO/IEC JTC 1/SC 27 to elevate supplier relationship security from best practice to explicit requirement.

Unlike SOC 2's principles-based Trust Services Criteria, ISO 27001 provides specific control objectives in its Annex A, supported by detailed implementation guidance in ISO 27002. This specificity benefits organizations seeking clear requirements but demands careful attention to the standard's expectations for supplier relationships. The 2022 revision reorganized controls into four themes—Organizational, People, Physical, and Technological—with supplier relationship controls now consolidated within the Organizational theme, emphasizing that supply chain security is a governance concern requiring management attention and organizational commitment.

Annex A Supplier Relationship Controls Overview¶

ISO 27001:2022 Annex A includes five controls specifically addressing supplier relationships, numbered A.5.19 through A.5.23. Together, these controls establish a comprehensive framework for managing security throughout the supplier lifecycle—from initial engagement through ongoing monitoring to relationship termination.

The 2022 revision significantly strengthened A.5.21: Managing information security in the ICT supply chain (replacing 2013's A.15.1.3), with expanded emphasis on component authenticity, integrity verification, and supplier security obligations. This enhancement reflects the SolarWinds compromise (2020) and similar incidents that demonstrated how ICT supply chain attacks can bypass traditional security controls.

A.5.19: Information Security in Supplier Relationships¶

A.5.19 requires organizations to define and implement processes for managing information security risks associated with suppliers. This control establishes the policy foundation for all supplier security activities.

ISO 27002:2022 guidance indicates organizations should:

• Identify and document types of suppliers and services requiring security consideration
• Establish criteria for supplier evaluation and selection based on security capability
• Define processes for assessing supplier security before engagement
• Maintain an inventory of suppliers with access to organizational information or systems
• Classify suppliers based on risk level and criticality

For software supply chain purposes, this control extends beyond traditional service providers to encompass:

• Commercial software vendors
• Open source projects whose components you use
• Development tool and platform providers
• Package registries and repositories

Your SBOM provides the foundation for supplier inventory in the software domain. Organizations should integrate component inventory with broader supplier management processes, applying consistent risk classification and assessment approaches.

Implementation evidence expected by auditors includes:

• Supplier security policy document
• Supplier classification criteria and risk assessment methodology
• Current supplier inventory with risk classifications
• Evidence of supplier security evaluation before engagement

A.5.20: Addressing Information Security Within Supplier Agreements¶

A.5.20 requires establishing and agreeing on relevant information security requirements with each supplier. This control ensures security expectations are documented and legally binding.

Required agreement elements include:

• Description of information and services to be provided or accessed
• Classification of information involved
• Legal and regulatory requirements applicable to supplier activities
• Security controls the supplier must implement
• Incident notification and response requirements
• Right to audit or assess supplier security
• Requirements for secure return or destruction of information at relationship end
• Supplier obligations regarding subcontractors

For software components, formal agreements present challenges. Commercial software typically comes with license agreements that may or may not address security. Open source components come with licenses addressing intellectual property but rarely security commitments.

This creates a practical dilemma during ISO 27001 certification audits. An auditor examining A.5.20 compliance asks: "Show me your supplier agreements with security requirements." The organization provides contracts with AWS, GitHub, and commercial vendors—all including security clauses. The auditor then asks about the 200 npm packages in the application. "What are your security agreements with those suppliers?" There are none. The MIT License doesn't commit the maintainer to patch vulnerabilities or even maintain the project.

Organizations address this gap through:

• Evaluating component security posture independently (since contractual assurance is unavailable)
• Establishing internal acceptance criteria substituting for supplier commitments
• Selecting components from projects with documented security practices (security policy, vulnerability disclosure process, active maintenance)
• Maintaining capability to respond to vulnerabilities without supplier assistance (forking, patching, replacing)

Auditors increasingly recognize that open source licensing models differ from traditional supplier agreements. Document your alternative approach—how do you achieve equivalent assurance when formal agreements aren't available? Create a policy defining minimum component acceptance criteria (e.g., "Components must be from projects with documented security contact information and evidence of security issue response within 90 days"). This demonstrates systematic risk management even when contracts are unavailable.

A.5.21: Managing Information Security in the ICT Supply Chain¶

A.5.21 specifically addresses information and communications technology (ICT) supply chain risks, requiring organizations to define and implement processes for managing information security risks associated with the ICT products and services supply chain. This control, strengthened in the 2022 revision, most directly addresses software supply chain security.

ISO 27002 guidance specifies attention to:

• Propagation of security requirements through the supply chain to subcontractors
• Security of the ICT product and service development lifecycle
• Component tracking and traceability
• Verification that delivered products and services conform to security requirements
• Monitoring for and management of components with known vulnerabilities
• Authentication of critical components

For software supply chains specifically, implementation should address:

Component provenance and integrity - Verifying components come from claimed sources - Validating component integrity through signatures and checksums - Tracking component versions and sources

Vulnerability management - Continuous monitoring for vulnerabilities in components - Defined processes for vulnerability response - Criteria for acceptable vulnerability risk

Build and deployment security - Securing build environments against tampering - Verifying build outputs match expected artifacts - Protecting deployment pipelines

Transitive dependencies - Visibility into indirect dependencies - Assessment of transitive dependency risks - Response capability for deeply nested vulnerabilities

This control provides the clearest alignment point for technical supply chain security practices within ISO 27001. Organizations should map SBOM generation, vulnerability scanning, and dependency management practices directly to A.5.21 requirements.

A.5.22: Monitoring, Review and Change Management of Supplier Services¶

A.5.22 requires organizations to regularly monitor, review, and manage changes to supplier services and their information security practices. This control addresses the ongoing nature of supplier relationships—initial assessment is insufficient without continuous oversight.

Required activities include:

• Monitoring supplier service performance and security
• Reviewing supplier security practices periodically
• Managing changes to supplier services, including:
• Changes to supplier security capabilities
• Updates to services or service levels
• Changes in supplier personnel with access
• Supplier incidents affecting the organization

For software components, ongoing monitoring translates to:

• Vulnerability monitoring: Continuous scanning for newly disclosed vulnerabilities affecting components in use
• Project health assessment: Periodic review of component project status (maintenance activity, responsiveness to security issues)
• Version currency: Tracking whether components are current or falling behind supported versions
• Change impact assessment: Evaluating security implications of dependency updates

Automated tools support these requirements:

• Dependency scanning tools (Snyk, Dependabot, Renovate) for vulnerability monitoring
• SBOM platforms (Dependency-Track) for component inventory and tracking
• Project health tools (OpenSSF Scorecard) for periodic assessment

Document monitoring frequency and thresholds. Auditors expect evidence that monitoring occurs consistently—scan reports, remediation tickets, and periodic assessment records demonstrate operating effectiveness.

A.5.23: Information Security for Use of Cloud Services¶

A.5.23 addresses cloud service security, requiring organizations to establish processes for acquisition, use, management, and exit from cloud services. While focused on cloud providers, this control intersects with supply chain security when considering:

• Package registries and artifact repositories hosted as cloud services
• CI/CD platforms (GitHub Actions, GitLab CI, CircleCI)
• Development tools and services
• Cloud-based security scanning services

Control requirements include:

• Defining security requirements for cloud service selection
• Establishing criteria for cloud service provider evaluation
• Managing security configuration of cloud services
• Addressing data location and jurisdictional concerns
• Planning for cloud service provider exit or failure

Organizations should ensure their cloud-hosted development and supply chain infrastructure receives the same security attention as production cloud services. A compromised CI/CD platform presents supply chain risks equivalent to a compromised build server.

Risk Assessment Integration¶

ISO 27001 requires organizations to perform information security risk assessments that identify risks, analyze their likelihood and impact, and determine appropriate treatments. Supply chain risks should be explicitly incorporated into this risk assessment process.

Identifying supply chain risks:

• Review component inventory for critical dependencies
• Assess exposure to single points of failure (heavily depended-upon components)
• Consider scenarios: What if a critical dependency becomes compromised? Abandoned? Unavailable?
• Evaluate risks from development tools and infrastructure, not just runtime dependencies

Risk analysis considerations:

• Likelihood: How probable is compromise or failure of this component?
• Impact: What would be the effect on your systems and customers?
• Existing controls: What mitigations are already in place?
• Residual risk: What risk remains after controls?

Risk treatment options:

• Avoid: Don't use components presenting unacceptable risk
• Modify: Implement additional controls (monitoring, sandboxing, fallback options)
• Share: Transfer risk through insurance or contractual arrangements
• Accept: Document acceptance of residual risk with appropriate authorization

Document supply chain risks in your risk register with the same rigor applied to other information security risks. Auditors will examine whether your risk assessment comprehensively addresses supplier and supply chain scenarios.

Certification Body Expectations¶

Certification audits assess both control implementation and operating effectiveness. For supplier relationship controls, auditors typically expect:

The certification process varies by certification body, but all must adhere to ISO/IEC 27006 accreditation requirements. Organizations often encounter variation in how auditors interpret supplier controls—particularly for software components. An organization certified by one body might face minimal scrutiny of their dependency management, while another body's auditors might conduct detailed technical assessment of SBOM processes and vulnerability remediation. This inconsistency has prompted calls for more specific guidance on applying supplier controls to modern software development practices.

Policy documentation: - Supplier security policy addressing A.5.19 requirements - Procedures for supplier assessment, agreements, monitoring, and cloud services - Integration with overall ISMS documentation

Supplier inventory: - Complete inventory of suppliers with security relevance - Risk classification for each supplier - Evidence of assessment before engagement

Contractual evidence: - Supplier agreements incorporating security requirements - Documentation of security terms in contracts - For open source, documented alternative approach to assurance

Monitoring evidence: - Records of ongoing supplier monitoring - Periodic assessment reports - Incident records related to supplier issues - Evidence of change management for supplier services

ICT supply chain specific: - Software component inventory (SBOM) - Vulnerability scanning reports - Evidence of provenance verification - Build and deployment security documentation

Certification bodies vary in their supply chain security sophistication. Some auditors have deep familiarity with software supply chain practices; others approach these controls through traditional vendor management lenses. Prepare to explain technical controls in terms the auditor understands, mapping to specific Annex A requirements.

ISMS Integration Strategies¶

Effective supply chain security requires integration across your Information Security Management System (ISMS), not isolated controls. Consider these integration points:

Asset management: Extend asset inventory to include software components. Your SBOM should feed into asset management processes, with components receiving the same classification and ownership assignment as other information assets.

Risk management: Incorporate supply chain scenarios into risk assessment methodology. Ensure risk criteria address supply chain-specific factors like component maintenance status and dependency depth.

Access control: Apply access control principles to supply chain infrastructure—who can modify dependencies, access build systems, or configure package sources?

Operations security: Include supply chain monitoring in operational security procedures. Vulnerability scanning should be as routine as other security monitoring activities.

Incident management: Extend incident response procedures to address supply chain compromise scenarios. Define escalation paths and response actions for dependency vulnerabilities and supply chain attacks.

Compliance: Map supply chain controls to other applicable frameworks (SOC 2, NIST, regulatory requirements). Unified control implementation reduces duplication while ensuring comprehensive coverage.

We recommend organizations:

1. Review all five supplier controls (A.5.19-A.5.23) as an integrated cluster rather than isolated requirements

2. Extend supplier inventory to include software components, using SBOMs as the authoritative source

3. Document alternative assurance approaches for open source components where formal agreements are unavailable

4. Integrate supply chain risk into your ISMS risk assessment process with specific supply chain scenarios

5. Implement continuous monitoring for dependencies, generating evidence of ongoing oversight throughout the certification period

6. Prepare auditor education materials explaining how technical supply chain controls satisfy Annex A requirements

7. Map to complementary frameworks (OWASP SCVS, NIST SSDF) that provide implementation detail beyond ISO 27002 guidance

ISO 27001:2022's strengthened supplier relationship controls reflect the maturation of supply chain security as a critical discipline. Organizations that integrate supply chain security throughout their ISMS will find certification validates genuine capability rather than creating compliance overhead.