ISO 27001
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ISO 27001 Internal vs External Audits Explained: Roles & Process

[
07 Dec 2025
]
By
Cariel Cohen

In the world of information security, ISO 27001 stands as a hallmark of excellence, demonstrating an organization's commitment to safeguarding sensitive data and maintaining robust information security management systems (ISMS). To achieve ISO 27001 certification, organizations must undergo a thorough audit process. However, here's where the journey diverges into two distinct paths: internal audits and external audits.

Understanding these differences is essential for anyone embarking on the ISO 27001 compliance journey or seeking to gain insights into how information security is upheld within an organization.

In this blog post, we'll delve into the critical distinctions between internal and external ISO 27001 audits, shedding light on their unique purposes, the roles of auditors, and the scope of assessments. Whether you're a seasoned information security professional or just beginning to explore the world of ISO 27001, this guide will provide valuable clarity on the intricacies of these vital assessments.

Why is ISO/IEC 27001 important?

As cyber threats continue to evolve and increase in frequency, managing information security risks has become more complex for organizations of all sizes. ISO/IEC 27001 supports a risk-based approach to security by helping organizations identify vulnerabilities early and take proactive steps to reduce exposure.

The standard encourages a comprehensive view of information security by addressing people, processes, and technology together. When implemented effectively, an ISO/IEC 27001–aligned information security management system (ISMS) serves as a structured framework for ongoing risk management, improved cyber resilience, and stronger operational practices. (2)

Purpose for ISO 27001 Audits:

Internal Audit (ISO 27001):

Internal ISO 27001 audits are designed to evaluate and enhance an organization’s information security management system (ISMS), ensuring compliance with ISO 27001 standards and highlighting areas for improvement, whether conducted by internal staff or an independent third party (1).

External Audit (ISO 27001):

External ISO 27001 audits are typically conducted by certification bodies or registrars to provide an independent assessment of an organization's ISMS and determine its eligibility for ISO 27001 certification.

Auditor Independence for ISO 27001 Audits:

Internal Auditor Independence (ISO 27001)

Internal ISO 27001 auditors should be independent and impartial within the organization, but they are still employees or contractors of the organization.

External Auditor Independence (ISO 27001)

External ISO 27001 auditors are completely independent of the organization and are hired by certification bodies to assess compliance with ISO 27001.

Scope for ISO 27001 Audits:

Internal Audit Scope (ISO 27001)

The scope of internal ISO 27001 audits includes assessing all relevant aspects of the organization's ISMS, such as policies, procedures, controls, and risk management practices.

External Audit Scope (ISO 27001):

External ISO 27001 audits focus on evaluating the organization's ISMS in accordance with ISO 27001 requirements and determining whether it meets the standard's criteria for certification.

Steps in an Internal ISO 27001 Audit

An internal ISO 27001 audit is a key part of maintaining an effective information security management system (ISMS) and preparing for certification. Following a structured process ensures all controls are reviewed, gaps are identified, and compliance is continuously improved. Below is a practical guide to the main steps in an internal audit.

1) Plan the Internal Audit

Careful planning sets the foundation for a successful audit.

Audit Plan Creation: Begin by drafting a detailed audit plan that defines the scope, objectives, and methodology. This blueprint guides the audit and ensures a systematic review of your ISMS.

Plan Updates: Regularly revisit the plan to account for changes in processes, risks, or regulatory requirements. Keeping the plan flexible ensures the audit stays relevant and effective.

2) Conduct the Internal Audit

This is the execution phase where controls and processes are evaluated.

Identify Control Owners: Determine who is responsible for specific ISMS controls and establish clear communication channels.

Audit Approach: Choose the methods to use interviews, document reviews, or observations—based on audit objectives and organizational context.

Audit Meetings: Schedule and conduct meetings with control owners to clarify scope, timeline, and expectations.

Evidence Collection: Review documentation and observe processes to gather evidence of compliance. Highlight gaps, risks, and areas for improvement.

3) Report Audit Findings

Sharing results ensures transparency and supports decision-making.

Report to Stakeholders: Provide clear findings to the auditee and management review team, including strengths, weaknesses, and recommended corrective actions.

4) Update Incident and Corrective Action Logs

Maintain a central log for all identified issues and follow-up actions. This supports continuous improvement and proactive risk management.

5) Refine the Audit Schedule

Adjust future audits based on current findings, shifting risks, and changes in organizational priorities. A dynamic schedule ensures ongoing compliance and strengthens the ISMS over time.

ISO 27001 External Audit Steps

External ISO 27001 audits are performed by certification bodies or independent parties to provide assurance that an organization’s ISMS is effective and compliant. These audits are critical for gaining, maintaining, and renewing ISO 27001 certification. While interested parties may observe or request audits, only an accredited certification body can formally certify an organization.

1) Plan the External Audit

Before the audit, external auditors coordinate with the organization to finalize an audit plan.

Audit Preparation: Resources are allocated, dates and times are set, and the scope is defined. This ensures that both auditors and the organization are aligned and prepared for the assessment.

2) Stage 1 Audit – Documentation Review

This initial review checks that the ISMS is properly established and documented.

Documentation Verification: External auditors assess whether all relevant policies, procedures, and records are in place, providing a foundation for the full certification audit.

3) Stage 2 Audit – Certification Audit

A detailed, fact-based audit evaluates whether the ISMS operates in accordance with ISO 27001 standards.

Operational Assessment: Auditors examine a representative sample of processes, observe implementation of controls, and verify that documented procedures are followed effectively.

4) Surveillance Audit

Periodic audits are conducted between certification and recertification to monitor ongoing compliance.

Focused Assessment: These audits review specific areas of the ISMS, ensuring corrective actions are maintained and risks are controlled.

5) Recertification Audit

A comprehensive audit performed before the end of the certification cycle, typically every three years.

Full ISMS Review: This stage covers all standard requirements, confirming that the organization continues to meet ISO 27001 standards and maintain a robust information security posture.

In conclusion, mastering ISO 27001 internal audits is not just about ticking boxes; it's about ensuring the robustness of your Information Security Management System and safeguarding the digital assets your organization holds dear. By adhering to the principles and best practices outlined in this blog post, you're not only meeting compliance requirements but also fortifying your defenses against the ever-evolving landscape of cyber threats.

Frequently Asked Questions (FAQ)

What is an ISO 27001 risk assessment?

An ISO 27001 risk assessment is a core part of the ISMS audit and helps organizations identify, analyze, and prioritize information security risks. It evaluates threats to information assets, the effectiveness of existing security controls, and potential impacts on business processes. The results feed directly into a risk treatment plan, supporting risk reduction and maintaining information security over time.

Who can perform an ISO 27001 audit?

ISO 27001 audits may be performed by different parties depending on the audit type. Internal audits are typically conducted by qualified internal auditors, consultants, or members of an audit team who are independent from the processes being reviewed. Certification audits, including the initial certification audit and recertification audits, must be conducted by an accredited certification body, often overseen by organizations such as the ANSI National Accreditation Board.

How often should ISO 27001 audits be conducted?

Organizations undergo internal audits at planned intervals, usually at least once per year, to support ongoing compliance and continual improvement. External audits follow a structured certification process that includes the initial certification audit, followed by periodic surveillance audits and recertification audits every three years to verify compliance and operating effectiveness.

What is included in an ISO 27001 internal audit report?

An internal audit report documents audit findings, evidence collection, and results of the internal audit process. It typically includes an executive summary, audit scope, document review outcomes, identified gaps, corrective actions, and recommendations for improvement. Audit logs and audit results help management review performance and strengthen the organization’s security posture.

How should organizations prepare for an ISO 27001 audit?

Effective audit preparation includes conducting a gap analysis, defining an audit plan, assigning process owners, and ensuring relevant organizational processes are documented. Regular internal audits, security awareness training, and strong security practices improve audit readiness and help prove compliance during audit execution, including remote audits where applicable.

How does ISO 27001 support long-term compliance?

ISO 27001 is designed to support maintaining compliance through continual improvement rather than one-time certification. Activities such as internal review, management review, audit programs, and monitoring contractual requirements help organizations maintain compliance, adapt to new security risks, and align information security with business strategy over time.

Why is ISO 27001 considered a key component of information security?

ISO 27001 provides a structured framework for managing information security risks across people, technology, and processes. By improving security posture, preventing data breaches, and strengthening operating effectiveness, it helps organizations achieve certification and demonstrate commitment to information security management over the long term.

Sources:

  1. Vanta, ISO 27001 internal audit, https://www.vanta.com/glossary/iso-27001-internal-audit 
  2. ISO, ISO/IEC 27001: Information security management, https://www.iso.org/standard/27001
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