ISO 27001 Independent Review of Information Security Explained

Security programmes drift when they are never challenged. Over my 30 years in governance, risk, and compliance, I have seen far too many organisations fall into the trap of self-validation, assuming that because their internal IT team built a control, it must be running effectively. Over time, operational shortcuts become habits, controls become outdated, and blind spots multiply quietly. Internal confidence alone is never a reliable indicator of security posture. Annex A 5.35 is about stepping back to get objective, unbiased assurance before a real-world incident or certification auditor forces the issue.

ISO 27001:2022 includes Annex A 5.35 to ensure your business periodically subjects its Information Security Management System (ISMS), policies, and operational controls to independent review. This control replaces former 2013 requirements (18.2.1) and emphasizes that assurance must be conducted by competent personnel who are functionally separate from the day-to-day operations they are evaluating.

Quick Summary: What ISO 27001 Annex A 5.35 Requires

At a practical level, Annex A 5.35 is about verifying that your security arrangements remain effective, fit for purpose, and aligned with organizational objectives. It does not mean you must hire expensive Big Four consultants every month; it expects independent, competent, and risk-proportionate reviews. Here is what you need to do in plain English:

Establish an Independent Review Schedule: Plan objective security reviews at regular, defined intervals (at least annually) and following major organizational or technical changes.
Ensure True Reviewer Independence: Select reviewers—whether internal staff from another department or external specialists—who have zero operational responsibility for the controls being audited.
Verify Reviewer Competence: Ensure the individuals conducting the review possess verified technical, operational, and auditing competence in ISO 27001 frameworks.
Define Risk-Based Review Scopes: Focus reviews on high-risk technical controls, critical business processes, policy compliance (Annex A 5.36), and incident response readiness.
Report Findings to Senior Leadership: Present objective review reports directly to executive management and the ISMS steering committee.
Track Corrective Action Plans: Convert review findings into formal corrective action tickets, assign explicit owners, and verify remediation effectiveness.

Why Self-Validation Is a Critical Security Hazard

When security teams audit their own work, cognitive bias and operational familiarity obscure obvious flaws. Teams naturally defend systems they designed, overlook long-standing workarounds, and assume legacy configurations are still secure simply because “nothing has broken yet.”

Ignoring independent review controls exposes your business to severe hazards:

Unnoticed Control Drift & Degradation: Security controls quietly degrading over time (e.g., firewall rules cluttering, backup restores failing, offboarding steps missed) without management awareness (Annex A 5.37).
Unchecked Executive & Operational Blind Spots: Overestimating security maturity based on optimistic internal reports rather than empirical evidence.
Certification Audit Failure: Experiencing major non-conformities during formal ISO 27001 stage 2 or surveillance audits because internal self-audits were superficial or biased.
Delayed Vulnerability Discovery: Uncovering critical architectural weaknesses only after an external cyber attack or ransomware breach occurs.

My 8 Step Plan to Implement Annex A 5.35 Fast

You do not need a multi-million-pound audit budget to satisfy an ISO 27001 auditor. Here is my pragmatic, 8-step plan to establish an audit-ready independent review framework.

1. Define the Independent Review Charter and Scope

Document a formal review charter outlining how independent reviews are commissioned, structured, and reported:

Specify the review scope: ISMS policies, risk assessments, technical control baselines (Annex A 8.9), supplier management (Annex A 8.30), and physical facilities.
Establish explicit review triggers: annual scheduled reviews, major infrastructure migrations, post-incident reviews, or significant corporate M&A.
Define governance escalation paths for reporting critical security gaps directly to the Board or executive leads.

2. Guarantee True Reviewer Independence

The core requirement of Annex A 5.35 is that no individual may review their own work or operational domain:

Internal Peer Reviews: Utilize qualified internal auditors or compliance leads from non-IT departments (e.g., Risk, Legal, Quality Assurance) who do not manage IT systems.
Reciprocal Department Audits: Use cross-functional auditing where team A audits team B’s processes and vice-versa, provided operational separation is maintained.
External Assurance Providers: Engage independent third-party ISO 27001 consultants, penetration testers, or specialized vCISO advisors for high-risk technical domains.

3. Verify Reviewer Technical and Auditing Competence

Independence without technical and governance competence produces superficial “box-checking” audits that add zero value:

Ensure reviewers possess recognized auditing qualifications (e.g., ISO 27001 Lead Auditor, CISA, CISSP).
Verify that reviewers understand your operational context, cloud architecture, regulatory obligations, and business objectives.
Maintain reviewer CVs, training records, and certification credentials inside your ISMS audit file as evidence.

4. Combine Governance Reviews with Technical Verification

An effective independent review must evaluate both written policy intent and real-world technical execution:

Governance & Process Review: Evaluate policy alignment, risk register accuracy, training completion logs (Annex A 6.3), and management review records.
Technical Validation & Sampling: Perform spot-checks on Active Directory / IdP access rights (Annex A 8.3), firewall rule sets, endpoint encryption health, and backup restore logs (Annex A 8.13).
Penetration Testing & Vulnerability Assessment: Incorporate external penetration testing and technical vulnerability scans (Annex A 8.8) into the review schedule.

5. Execute Ad-Hoc Reviews Following Major Organizational Changes

Do not wait for the annual review cycle if your operating environment undergoes significant structural shifts:

Commission immediate ad-hoc independent reviews following a major cloud migration, network re-architecture, or core platform shift.
Trigger independent assessments following major security incidents (Annex A 6.8) to evaluate response effectiveness and control failures.
Re-review physical and logical security perimeters whenever new office facilities or data centers are onboarded (Annex A 7.1).

6. Standardize Audit Evidence Collection and Working Papers

Ensure independent review findings are grounded strictly in verifiable, objective evidence rather than hearsay:

Require reviewers to document explicit evidence samples (screenshots, log extracts, configuration files, interview notes) for every finding.
Categorize review findings using clear risk ratings: Critical, Major Non-Conformity, Minor Non-Conformity, or Opportunity for Improvement (OFI).
Maintain secure, access-controlled audit working paper archives to demonstrate thoroughness to external certification bodies.

7. Report Findings Directly to Executive Management

Independent review outputs must reach leadership directly without operational filtering or suppression:

Present comprehensive review reports directly to the CISO, CEO, Audit Committee, or ISMS Steering Committee.
Highlight systemic risks, resource bottlenecks, and strategic security gaps alongside technical non-conformities.
Obtain executive sign-off and management commitment for proposed remediation budgets and timelines.

8. Track Corrective Action Plans to Closure

A review that generates a report but drives no concrete operational change is completely useless:

Log all review non-conformities and improvement opportunities inside your central Corrective Action Register.
Assign explicit operational leads, remediation milestones, and target completion dates to every action item.
Re-audit high-risk findings 30–90 days post-remediation to verify that corrective actions eliminated the root cause before closing the issue (Annex A 5.36).

Common Implementation Pitfalls and How to Fix Them

When preparing clients for ISO 27001 audits, I frequently spot the same independent review mistakes. Here are the main traps and how to solve them:

Problem: The IT Manager Auditing Their Own Firewall Configurations and User Access Logs
Ninja Solution: Assign internal audit duties to an independent quality lead, cross-department auditor, or external third-party consultant.
Problem: Conducting “Paper-Only” Reviews That Read Policies Without Verifying Systems
Ninja Solution: Mandate evidence-based sampling—require the reviewer to inspect live console configurations, access logs, and backup tests.
Problem: Review Reports Sitting Unaddressed in an Email Inbox Without Corrective Action Tracking
Ninja Solution: Feed every audit finding directly into a tracked ISMS Corrective Action Register with mandatory executive progress reporting.
Problem: Treating Independent Reviews as a Fault-Finding Expedition to Punish Staff
Ninja Solution: Frame reviews as constructive, risk-reduction exercises designed to improve system resilience and secure executive support.

The ISO 27001 Ninja Bottom Line

ISO 27001 Annex A 5.35 is about maintaining objective assurance over your security posture over time. Internal confidence and self-validation are dangerous illusions; independent, evidence-based reviews ensure your controls remain active, relevant, and fully aligned with operational reality.

By establishing a clear review charter, ensuring strict reviewer independence, verifying auditor competence, combining policy reviews with technical sampling, executing ad-hoc reviews after major changes, reporting findings directly to executive leadership, and tracking corrective actions to verified closure, you eliminate security blind spots, foster continuous ISMS improvement, and satisfy your ISO 27001 auditor with complete confidence.