In this ultimate how to audit guide to ISO 27001 Annex A 5.25 Assessment and Decision on Information Security Events, you will learn directly from an ISO 27001 Lead Auditor:
- 10 Key Audit Steps
- Verification Criteria
- Required Evidence
- The Pass / Fail Test
I am Stuart Barker, the ISO 27001 Lead Auditor and author of the Ultimate ISO 27001 Toolkit.
Using over 30 years of industry experience across hundreds of audits, I’m giving you the exact templates, walkthroughs, and practical examples you need to achieve ISO 27001 certification.
Table of contents
- 1. Security Event Assessment Methodology Formalisation Verified
- 2. Point of Contact (PoC) for Event Reporting Confirmed
- 3. Event Logging Integrity and Completeness Validated
- 4. Triage and Decision-Making Timelines Verified
- 5. Technical Assessment Competence Alignment Confirmed
- 6. False Positive Documentation and Justification Verified
- 7. Escalation Trigger Points and Thresholds Validated
- 8. Incident Declaration Records and Handover Confirmed
- 9. Multi-Source Event Correlation Evidence Identified
- 10. Periodic Review of Assessment Accuracy Verified
Auditing ISO 27001 Annex A 5.25 Assessment and Decision on Information Security Events verifies the systematic evaluation of security anomalies to determine if they constitute an incident. This process validates the Primary Implementation Requirement of triaging events against established criteria to prevent false positives and missed threats. The Business Benefit ensures optimal resource allocation by filtering noise and focusing response efforts on genuine security risks.
1. Security Event Assessment Methodology Formalisation Verified
Verification Criteria: A documented methodology exists that defines the objective criteria for assessing whether a security event should be classified as a security incident.
Required Evidence: Approved Incident Management Procedure containing a “Decision Tree” or “Assessment Matrix” for event-to-incident conversion.
Pass/Fail Test: If the organisation relies on the subjective “gut feeling” of IT staff rather than a documented classification rubric, mark as Non-Compliant.
2. Point of Contact (PoC) for Event Reporting Confirmed
Verification Criteria: A specific, singular point of contact or function (e.g., SOC, Helpdesk) is designated and available to receive and log all security events.
Required Evidence: Service Desk configuration or “Contact Us” security portal documentation showing a central intake for all events.
Pass/Fail Test: If security events are sent to multiple uncoordinated personal mailboxes without a central tracking ID, mark as Non-Compliant.
3. Event Logging Integrity and Completeness Validated
Verification Criteria: Every reported security event is recorded with a unique ID, timestamp, reporter details, and a description of the observed anomaly.
Required Evidence: Sample of 10 “Low” or “Informational” events from the ITSM tool or SIEM (Security Information and Event Management) system.
Pass/Fail Test: If an event was reported but no record of its initial assessment exists in the ticketing system, mark as Non-Compliant.
