ISO 27001:2022 Annex A 8.21 – Security of Network Services Explained

Networks are only as secure as the services running on them.
If network services are weak, protected systems quickly become irrelevant.

Annex A 8.21 exists to ensure organisations secure network services themselves, not just the underlying networks, preventing unauthorised access, misuse, disruption, and compromise.

This control is about securing what the network delivers, not just how it is connected.

ISO 27001

Quick Guide: Annex A 8.21 at a Glance

Annex A 8.21 of ISO 27001:2022 focuses on security of network services.

At a practical level, this means:

  • Securing internal and external network services
  • Defining access rules for who can use services, from where and when
  • Applying authentication, authorisation, and encryption
  • Monitoring use of network services
  • Ensuring providers meet defined security requirements

The control applies to services, not just infrastructure.

In-Depth Guide to Annex A 8.21

What Is Annex A 8.21 and Why Does It Matter?

A network service is any service delivered over a network, including:

  • Email services
  • File and print services
  • Directory and authentication services
  • Managed applications
  • Firewalls, intrusion detection, and security platforms
  • Remote access and connectivity services

These services are often:

  • Shared
  • Externally exposed
  • Business-critical

If network services are insecure:

  • Unauthorised users gain access
  • Data may be intercepted or altered
  • Services may be abused or disrupted
  • Attackers bypass network-level controls

Annex A 8.21 ensures organisations treat network services as security-critical assets, not background infrastructure.

This control replaces ISO 27001:2013 Annex A 13.1.2 and expands emphasis on service-level security and accountability.

How to Implement Annex A 8.21 Effectively

A pragmatic approach to Annex A 8.21 typically includes the following elements.

1. Identify Network Services in Scope

Organisations should identify:

  • Internal network services
  • Internet-facing services
  • Third-party or managed network services

Security cannot be applied to services that are not known.

2. Define Security Requirements for Network Services

Each network service should have defined security requirements, including:

  • Authentication requirements
  • Access restrictions
  • Encryption expectations
  • Availability and resilience needs

Requirements should reflect:

  • Information sensitivity
  • Business criticality
  • Exposure risk
3. Control Access to Network Services

Access to network services should be:

  • Explicitly authorised
  • Based on business need
  • Approved and reviewed

Controls should define:

  • Who may access the service
  • From which locations or networks
  • At what times

Open access is rarely justified.

4. Apply Strong Authentication and Authorisation

Annex A 8.21 expects services to:

  • Authenticate users or systems securely
  • Enforce authorisation rules consistently

This may include:

  • Multi-factor authentication
  • Role-based access
  • Service-specific credentials

Service access should never rely on trust alone.

5. Protect Network Services Using Encryption

Where data is transmitted via network services, organisations should consider:

  • Encryption in transit
  • Secure communication protocols

Protection should reflect:

  • Data classification
  • Exposure to untrusted networks
  • Threat environment

Encryption protects both confidentiality and integrity.

6. Restrict and Filter Service Connectivity

Network services should:

  • Accept only required connections
  • Reject unnecessary protocols or sources
  • Be shielded from direct exposure where possible

Service-level restrictions complement network-level controls.

7. Monitor Use of Network Services

Annex A 8.21 explicitly supports monitoring.

Organisations should monitor:

  • Who accesses network services
  • When and from where
  • Abnormal usage patterns

Monitoring supports:

  • Detection of misuse
  • Incident investigation
  • Capacity and availability management

Unmonitored services are blind spots.

8. Log Network Service Access and Activity

Logs should record relevant service activity, such as:

  • Successful and failed access attempts
  • Administrative actions
  • Configuration changes

Logs support:

  • Accountability
  • Forensic investigation
  • Audit and assurance

This aligns closely with Annex A 8.15 (Logging).

9. Secure Network Services Provided by Third Parties

Where network services are provided externally, organisations should ensure:

  • Security requirements are defined contractually
  • Responsibilities are clearly allocated
  • Service performance and security are reviewed

Third-party services remain organisational risk.

10. Define and Monitor Service Levels

Annex A 8.21 highlights the importance of:

  • Service level requirements
  • Availability expectations
  • Performance and security metrics

Monitoring ensures providers and internal teams meet obligations consistently.

11. Manage Changes to Network Services

Changes to network services should:

  • Follow formal change management
  • Be tested before deployment
  • Be recorded and reviewed

Uncontrolled service changes are a common outage cause.

In-Depth Guide to Annex A 5.1

What is Annex A 5.1 and Why Does It Matter?

  • What the organisation values
  • How security decisions are approached
  • Where accountability sits
  • Aligns security with business objectives
  • Supports proportionate, risk-based decisions
  • Provides a reference point during incidents and disputes
  • Creates consistency without bureaucracy

How to Implement Annex A 5.1 Effectively

1. Define a Comprehensive Information Security Policy
  • Scope: What the policy applies to (systems, data, people).
  • Objectives: Why security is important for the business.
  • Roles & Responsibilities: Who is accountable for security.
  • Key Principles: Risk management, access control, and data protection.
2. Secure Senior Management Approval
  • Review and approve policies.
  • Ensure resources are allocated for implementation.
  • Lead by example in enforcing security policies.
3. Communicate and Train Employees
  • Include security policies in onboarding and ongoing training.
  • Ensure policies are easily accessible to all employees.
  • Encourage acknowledgment and acceptance of security responsibilities.
4. Regular Review & Continuous Improvement
  • Set a schedule for periodic policy reviews (at least annually).
  • Update policies based on business changes, new threats, or regulatory updates.
  • Conduct audits to ensure compliance and effectiveness.
5. Integrate Policies into the ISMS
  • Use it to develop more detailed security procedures.
  • Ensure policies align with other Annex A controls and broader risk management practices.
Key Differences: ISO 27001:2013 vs ISO 27001:2022
AspectISO 27001:2013ISO 27001:2022
Control StructureTwo separate controls: 5.1.1 & 5.1.2Merged into one control (5.1)
Implementation GuidanceLess prescriptiveMore detailed guidance for policy creation and alignment
Awareness & TrainingNot explicitly mentionedExplicitly requires policies to be part of training programmes
Attributes TableNot includedew attributes table for mapping policies to industry terms
Common Challenges & How to Overcome Them
  • Challenge: Employees don’t follow security policies.
  • Solution: Make policies practical and relevant to daily work. Use real-world examples in training.
  • Challenge: Policies are outdated or too generic.
  • Solution: Schedule annual reviews and update policies based on real threats and business changes.
  • Challenge: Policies are written in technical jargon.
  • Solution: Use plain language that all employees can understand.
  • Challenge: Lack of leadership buy-in.
  • Solution: Show how weak security affects business objectives—costs of breaches, loss of client trust, and legal penalties.
Final Recommendations
  • Make security policies living documents—review, refine, and update regularly.
  • Use policy training and awareness to create a security-conscious workforce.
  • Ensure policies are accessible, relevant, and easy to understand.
  • Keep policies aligned with business strategy and regulatory requirements.
  • Engage leadership in driving security culture from the top down.

Practical Considerations

Annex A 8.21 does not require:

  • Custom security for every minor service
  • Complex service management frameworks by default
  • Treating all services equally

It does require organisations to:

  • Secure services proportionate to their risk
  • Control and monitor service access
  • Be clear about who is responsible

Most network incidents involve services, not cables.

Common Challenges and How to Overcome Them

  • Assuming network security automatically secures services
  • Apply security controls at the service level
  • Unclear responsibility for managed services
  • Define ownership and contractual accountability
  • Services exposed without monitoring
  • Log and monitor service usage
  • Access granted without review
  • Periodically review service access rights

Network services fail when nobody owns them.

In-Depth Guide to Annex A 5.1

What is Annex A 5.1 and Why Does It Matter?

  • What the organisation values
  • How security decisions are approached
  • Where accountability sits
  • Aligns security with business objectives
  • Supports proportionate, risk-based decisions
  • Provides a reference point during incidents and disputes
  • Creates consistency without bureaucracy

How to Implement Annex A 5.1 Effectively

1. Define a Comprehensive Information Security Policy
  • Scope: What the policy applies to (systems, data, people).
  • Objectives: Why security is important for the business.
  • Roles & Responsibilities: Who is accountable for security.
  • Key Principles: Risk management, access control, and data protection.
2. Secure Senior Management Approval
  • Review and approve policies.
  • Ensure resources are allocated for implementation.
  • Lead by example in enforcing security policies.
3. Communicate and Train Employees
  • Include security policies in onboarding and ongoing training.
  • Ensure policies are easily accessible to all employees.
  • Encourage acknowledgment and acceptance of security responsibilities.
4. Regular Review & Continuous Improvement
  • Set a schedule for periodic policy reviews (at least annually).
  • Update policies based on business changes, new threats, or regulatory updates.
  • Conduct audits to ensure compliance and effectiveness.
5. Integrate Policies into the ISMS
  • Use it to develop more detailed security procedures.
  • Ensure policies align with other Annex A controls and broader risk management practices.
Key Differences: ISO 27001:2013 vs ISO 27001:2022
AspectISO 27001:2013ISO 27001:2022
Control StructureTwo separate controls: 5.1.1 & 5.1.2Merged into one control (5.1)
Implementation GuidanceLess prescriptiveMore detailed guidance for policy creation and alignment
Awareness & TrainingNot explicitly mentionedExplicitly requires policies to be part of training programmes
Attributes TableNot includedew attributes table for mapping policies to industry terms
Common Challenges & How to Overcome Them
  • Challenge: Employees don’t follow security policies.
  • Solution: Make policies practical and relevant to daily work. Use real-world examples in training.
  • Challenge: Policies are outdated or too generic.
  • Solution: Schedule annual reviews and update policies based on real threats and business changes.
  • Challenge: Policies are written in technical jargon.
  • Solution: Use plain language that all employees can understand.
  • Challenge: Lack of leadership buy-in.
  • Solution: Show how weak security affects business objectives—costs of breaches, loss of client trust, and legal penalties.
Final Recommendations
  • Make security policies living documents—review, refine, and update regularly.
  • Use policy training and awareness to create a security-conscious workforce.
  • Ensure policies are accessible, relevant, and easy to understand.
  • Keep policies aligned with business strategy and regulatory requirements.
  • Engage leadership in driving security culture from the top down.

Final Recommendations

Annex A 8.21 is about securing what actually delivers functionality to users and systems.

When network service security is implemented effectively:

  • Access is controlled and auditable
  • Misuse is detected earlier
  • Availability and reliability improve
  • Supplier and internal accountability are clearer

Networks connect systems.
Services make them usable.

Annex A 8.21 ensures those services are secure, controlled, and dependable.

In-Depth Guide to Annex A 5.1

What is Annex A 5.1 and Why Does It Matter?

  • What the organisation values
  • How security decisions are approached
  • Where accountability sits
  • Aligns security with business objectives
  • Supports proportionate, risk-based decisions
  • Provides a reference point during incidents and disputes
  • Creates consistency without bureaucracy

How to Implement Annex A 5.1 Effectively

1. Define a Comprehensive Information Security Policy
  • Scope: What the policy applies to (systems, data, people).
  • Objectives: Why security is important for the business.
  • Roles & Responsibilities: Who is accountable for security.
  • Key Principles: Risk management, access control, and data protection.
2. Secure Senior Management Approval
  • Review and approve policies.
  • Ensure resources are allocated for implementation.
  • Lead by example in enforcing security policies.
3. Communicate and Train Employees
  • Include security policies in onboarding and ongoing training.
  • Ensure policies are easily accessible to all employees.
  • Encourage acknowledgment and acceptance of security responsibilities.
4. Regular Review & Continuous Improvement
  • Set a schedule for periodic policy reviews (at least annually).
  • Update policies based on business changes, new threats, or regulatory updates.
  • Conduct audits to ensure compliance and effectiveness.
5. Integrate Policies into the ISMS
  • Use it to develop more detailed security procedures.
  • Ensure policies align with other Annex A controls and broader risk management practices.
Key Differences: ISO 27001:2013 vs ISO 27001:2022
AspectISO 27001:2013ISO 27001:2022
Control StructureTwo separate controls: 5.1.1 & 5.1.2Merged into one control (5.1)
Implementation GuidanceLess prescriptiveMore detailed guidance for policy creation and alignment
Awareness & TrainingNot explicitly mentionedExplicitly requires policies to be part of training programmes
Attributes TableNot includedew attributes table for mapping policies to industry terms
Common Challenges & How to Overcome Them
  • Challenge: Employees don’t follow security policies.
  • Solution: Make policies practical and relevant to daily work. Use real-world examples in training.
  • Challenge: Policies are outdated or too generic.
  • Solution: Schedule annual reviews and update policies based on real threats and business changes.
  • Challenge: Policies are written in technical jargon.
  • Solution: Use plain language that all employees can understand.
  • Challenge: Lack of leadership buy-in.
  • Solution: Show how weak security affects business objectives—costs of breaches, loss of client trust, and legal penalties.
Final Recommendations
  • Make security policies living documents—review, refine, and update regularly.
  • Use policy training and awareness to create a security-conscious workforce.
  • Ensure policies are accessible, relevant, and easy to understand.
  • Keep policies aligned with business strategy and regulatory requirements.
  • Engage leadership in driving security culture from the top down.

The Annex Control Table

ISO 27001:2022 Organisational Controls
ISO 27001:2022 Technological Controls