Annex A 5.19: Information Security in Supplier Relationships

Annex a 5.19: information security in supplier relationships requirement means you must manage information security risk introduced by third parties across the supplier lifecycle: selection, contracting, onboarding, ongoing monitoring, and offboarding. Operationalize it by setting supplier security requirements, assessing suppliers against them, embedding them in contracts, and keeping recurring evidence that the process runs. ¹

Key takeaways:

• Define and document supplier security requirements, then apply them consistently across third parties. ¹
• Tie requirements to contracts and measurable operating routines (intake, risk assessment, monitoring, exit). ¹
• Keep auditable evidence that the control operates: decisions, approvals, reviews, and exceptions. ¹

Annex A 5.19 sits at the point where your ISMS meets procurement, IT, and the business. It expects you to control the security exposure created by third parties that touch your data, systems, or facilities, not by “trusting” suppliers, but by setting requirements and proving you enforce them. For a Compliance Officer, CCO, or GRC lead, the fastest path is to treat 5.19 as an operating requirement: establish a supplier security standard, require risk-based due diligence before access is granted, contractually bind suppliers to your baseline controls, and monitor that those controls stay true over time. ¹

Most audit pain here comes from gaps between policy and practice. Teams often have a vendor risk policy, but no proof it is used for every relevant third party, or they have SOC reports collected in a folder with no documented review outcome. Annex A 5.19 rewards a simple, repeatable lifecycle with clear decision points, ownership, and evidence. If you can show a complete thread from third-party intake through assessment, contract clauses, onboarding approvals, periodic review, and termination, you can make this control routine rather than a fire drill. ¹

Regulatory text

Framework excerpt (provided): “ISO/IEC 27001:2022 Annex A control 5.19 implementation expectation (Information Security in Supplier Relationships).” ¹

Operator interpretation of what you must do:
You must govern information security risks created by supplier relationships by defining appropriate security requirements for third parties and ensuring those requirements are addressed across the relationship lifecycle (selection, contracting, delivery, and change/termination). You also need evidence that this is not ad hoc: it is a documented control that operates repeatedly and produces reviewable records. ¹

Plain-English interpretation (what 5.19 really demands)

Annex A 5.19 expects disciplined third-party risk management focused on information security:

• You decide what “secure enough” means for third parties that impact your confidentiality, integrity, or availability.
• You verify (through due diligence) whether a third party can meet those requirements before you share data or grant access.
• You bind the third party to those requirements (usually through contract terms and security schedules).
• You monitor and respond when something changes: scope, systems, subprocessors, incidents, control failures, or termination. ¹

If you only do questionnaires, you will fail in practice. If you only put clauses in contracts, you will fail in an audit. 5.19 expects both: control design (requirements) plus control operation (evidence of execution). ¹

Who it applies to (entity and operational context)

Applies to: Organizations running an ISMS aligned to ISO/IEC 27001 that use third parties in any capacity that can affect information security, including service providers, SaaS, MSPs, consultants, contractors, cloud platforms, and logistics providers with systems access or sensitive information exposure. ¹

Operational triggers (treat these as “in scope” by default):

• A third party stores, processes, transmits, or can access your information (including customer data).
• A third party connects to your network, identity provider, endpoints, or production systems.
• A third party provides a component that could affect service availability or integrity (outsourced operations, hosting, payment processing).
• A third party uses subprocessors to deliver the service (supply chain depth matters). ¹

What you actually need to do (step-by-step)

1) Define a supplier security standard (your baseline)

Create a short, controlled document that procurement and engineering can use. Include:

• Minimum security controls (access control, encryption expectations, vulnerability management, incident reporting expectations, logging, BCP/DR responsibilities).
• Data handling rules (classification, permitted locations if relevant, retention and deletion expectations).
• Subprocessor rules (approval/notification expectations).
• Evidence you will accept (SOC 2, ISO certificate, pen test summary, attestations) and how you review it.
• Exception process (who can approve deviations; how they are time-bounded and tracked). ¹

Keep it implementable. If you can’t enforce it, remove or reframe it into a risk decision.

2) Build an intake gate (so nothing bypasses security)

Operationalize a single path for onboarding third parties:

• Intake form captures: service description, data types, access method, hosting model, criticality, and whether the third party will use subprocessors.
• Gating rule: no production access, no data sharing, and no contract signature until security review completes or a documented exception is approved. ¹

This gate is your strongest audit story because it proves control over “shadow suppliers.”

3) Perform risk-based due diligence

Match diligence depth to risk. A simple tiering model works well:

• Low-risk: no sensitive data, no system access. Light review, basic contractual terms.
• Medium-risk: limited sensitive data or limited access. Questionnaire plus evidence review.
• High-risk: sensitive data, privileged access, or operational criticality. Deep review: independent reports, security architecture discussion, incident history, and clear remediation actions before go-live. ¹

Document the decision. Auditors want to see that you considered risk and chose an appropriate level of review.

4) Embed requirements into contracts (and make them enforceable)

Work with Legal and Procurement to standardize a security addendum or security schedule. Common elements:

• Confidentiality and data protection obligations aligned to your data classification.
• Incident notification and cooperation obligations.
• Right to audit or right to receive independent assurance reports.
• Subprocessor controls.
• Secure deletion/return at termination.
• Access control expectations for supplier personnel. ¹

Practical point: auditors often accept a clear clause library plus executed samples that show consistent use.

5) Onboard with technical controls, not just paperwork

Before go-live:

• Confirm least-privilege access, identity lifecycle, and authentication method.
• Validate data transfer paths and encryption expectations.
• Ensure operational contacts exist for security incidents and maintenance windows.
• Record “go-live approval” tied to the risk assessment and contract completion. ¹

6) Monitor suppliers and record outcomes

Monitoring can be lightweight, but it must exist:

• Track contract renewals and require re-review if scope or risk changes.
• Request updated assurance evidence on a defined cadence that fits your risk tier (your choice; document it as policy).
• Capture and disposition security events: incidents, control failures, adverse findings, or material service changes.
• Track exceptions and remediation commitments to closure. ¹

7) Manage offboarding and termination

Offboarding is part of the control:

• Revoke access (accounts, VPN, API keys, shared secrets).
• Confirm data return/deletion consistent with contract.
• Confirm asset return if applicable (badges, devices).
• Record closure evidence. ¹

Required evidence and artifacts to retain (audit-ready)

Keep evidence that shows both coverage (you didn’t miss suppliers) and operation (you reviewed and acted).

Core artifacts:

• Supplier inventory with owners, services, data/access notes, and risk tier.
• Supplier security standard / third-party security requirements document.
• Intake records (requests, scoping details, approval timestamps).
• Completed risk assessments (questionnaires, scored results, rationale, and sign-off).
• Evidence reviews (SOC/ISO certificates) with documented conclusions, not just files stored.
• Executed contracts with security clauses or referenced addenda.
• Exception register (deviations, compensating controls, approvals, expiry, closure).
• Ongoing monitoring records (review logs, renewal checks, change assessments).
• Offboarding checklists and access revocation evidence. ¹

Tip for serious operators: store these in a system that can produce an audit trail. Daydream-style workflows work well because they force structured intake, approvals, and recurring evidence capture mapped directly to Annex A 5.19. ¹

Common exam/audit questions and hangups

Auditors and certification bodies tend to probe the same weak points:

• “Show me your complete list of suppliers and how you determined which are in scope.” Hangup: inventory exists, but it’s incomplete or not tied to procurement/AP.
• “Pick a high-risk supplier and show end-to-end evidence from due diligence to contract to onboarding.” Hangup: documents exist, but no dated approval trail.
• “How do you ensure renewals and scope changes trigger a reassessment?” Hangup: monitoring is informal and not recorded.
• “How do you manage supplier incidents and corrective actions?” Hangup: issues are handled in email/Slack with no register or closure evidence.
• “How do you control subprocessors?” Hangup: contract mentions them, but no operational follow-up exists. ¹

Frequent implementation mistakes (and how to avoid them)

1. Confusing collection with review.
   Avoidance: require a documented reviewer conclusion for each assurance artifact and record any follow-ups. ¹

2. No gating control.
   Avoidance: enforce “no access/no data/no signature without security review or exception” and prove it with intake workflow logs. ¹

3. One-size-fits-all diligence.
   Avoidance: tier suppliers and tailor depth. Keep the tiering rationale in the record. ¹

4. Contracts drift from security requirements.
   Avoidance: maintain a clause library and require security addendum attachment for in-scope third parties. Sample executed agreements for audits. ¹

5. Offboarding ignored.
   Avoidance: tie termination steps to IAM tickets and deletion attestations where applicable. Keep closure evidence. ¹

Enforcement context and risk implications

Public enforcement case sources were not provided for this requirement, so don’t anchor your program on any specific regulator outcome here. Your practical risk is operational and audit-driven: suppliers are a common pathway for data exposure, service disruption, and incident response complexity, and Annex A 5.19 is where an ISO auditor expects you to show disciplined governance over that exposure. ¹

Practical 30/60/90-day execution plan

First 30 days (stabilize and stop bypass)

• Stand up (or clean up) the supplier inventory; reconcile with procurement and accounts payable exports.
• Publish a supplier security standard with a simple tiering approach.
• Implement an intake gate and exception path with named approvers.
• Select a small set of “critical/high-risk” suppliers and run the full workflow end-to-end to validate the process. ¹

Days 31–60 (contract + workflow hardening)

• Standardize security addendum language with Legal and Procurement.
• Create review templates: SOC/ISO review checklist, risk assessment record, onboarding approval record.
• Build a monitoring register for reassessments, renewals, and scope changes.
• Train procurement and business owners on the gate and what triggers security review. ¹

Days 61–90 (operationalize monitoring and prove it works)

• Run monitoring reviews for your top-tier suppliers and document outcomes.
• Test offboarding for a terminated supplier (or run a tabletop offboarding drill) and retain evidence.
• Audit your own process: sample suppliers and confirm each has intake, diligence, contract, and approval records.
• If you use Daydream, map Annex A 5.19 to the workflow steps and schedule recurring evidence capture so future audits pull from a single system of record. ¹

Frequently Asked Questions

Do we need to assess every supplier, even low-risk ones?

You need a method that identifies which third parties can affect information security and applies appropriate controls. For low-risk suppliers, that can mean a light-touch review plus baseline contract terms, but you should still record the decision. ¹

Are SOC 2 reports required to satisfy Annex A 5.19?

No specific assurance artifact is mandated by the provided text. What matters is that you define supplier security requirements, perform due diligence appropriate to risk, and retain evidence of your review and decisions. ¹

How do we handle suppliers that refuse our security addendum?

Treat it as a documented exception with explicit risk acceptance, compensating controls, and a time-bound plan (for example, re-negotiate at renewal). Keep the approval trail and the rationale. ¹

What’s the minimum evidence an auditor will want to see?

A supplier inventory, documented requirements, and several supplier samples showing end-to-end execution: assessment, contract clauses, onboarding approval, and monitoring/offboarding records. Files without review notes usually draw follow-up questions. ¹

Does Annex A 5.19 cover contractors and consultants, or only “vendors”?

Treat it as third-party scope. If a consultant or contractor can access systems or sensitive information, they are part of the supplier relationship risk you must manage under 5.19. ¹

How should we show “ongoing monitoring” without creating a huge program?

Start with a risk-tiered monitoring plan and record outcomes for the highest-impact suppliers first. A small number of well-documented reviews beats an aspirational schedule with no evidence. ¹

Footnotes

1. ISO/IEC 27001 overview; ISMS.online Annex A control index