ISO 27001 Annex A 5.25 Audit Checklist

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.

This technical verification tool is designed for lead auditors to establish the legitimacy of organisational incident response operations. Use this checklist to validate compliance with ISO 27001 Annex A 5.25 (Assessment and decision on information security events) by ensuring that every security event is systematically evaluated and triaged.

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.

4. Triage and Decision-Making Timelines Verified

Verification Criteria: Assessment of events occurs within a predefined timeframe (SLA) to minimise the window of potential impact before a formal incident is declared.

Required Evidence: Audit logs showing the delta between “Event Created” and “Assessment Completed” timestamps.

Pass/Fail Test: If high-priority events consistently exceed the documented assessment window without justification, mark as Non-Compliant.

5. Technical Assessment Competence Alignment Confirmed

Verification Criteria: Personnel responsible for the initial assessment of security events possess the technical training or experience required to differentiate between false positives and real threats.

Required Evidence: Training records for Tier 1 Analysts or Helpdesk staff specifically covering “Security Event Triage.”

Pass/Fail Test: If the staff performing initial triage have not received specific security awareness or technical triage training, mark as Non-Compliant.

6. False Positive Documentation and Justification Verified

Verification Criteria: Events assessed as “Non-Incidents” or “False Positives” include a brief technical justification for the decision to close the event.

Required Evidence: Closed event tickets showing comments such as “Benign activity: verified as authorized vulnerability scan” or similar technical detail.

Pass/Fail Test: If tickets are closed with generic “No action required” notes without a technical explanation, mark as Non-Compliant.

7. Escalation Trigger Points and Thresholds Validated

Verification Criteria: Specific triggers (e.g., failed login threshold, malware detection on critical asset) are documented that mandate immediate escalation to the Incident Response Team.

Required Evidence: SIEM correlation rule definitions or the “Escalation” section of the Incident Management Plan.

Pass/Fail Test: If the escalation path is purely manual and lacks automated thresholds for critical security events, mark as Non-Compliant.

8. Incident Declaration Records and Handover Confirmed

Verification Criteria: When an event is classified as an incident, a formal “Declaration” occurs, and the record is transitioned to the Incident Response workflow.

Required Evidence: Audit trail in the ticketing tool showing a change in record type from “Event/Alert” to “Incident” with a corresponding severity assignment.

Pass/Fail Test: If incidents are managed within the standard “Service Request” queue without a distinct security incident status, mark as Non-Compliant.

9. Multi-Source Event Correlation Evidence Identified

Verification Criteria: The assessment process considers multiple data points (e.g., logs, user reports, threat intel) to determine the legitimacy of an event.

Required Evidence: Security Analyst work-notes showing the cross-referencing of a user report against firewall or endpoint logs.

Pass/Fail Test: If assessments are performed solely on the basis of a user’s description without verifying technical log data, mark as Non-Compliant.

10. Periodic Review of Assessment Accuracy Verified

Verification Criteria: Management or a Senior Analyst periodically reviews closed “Events” to ensure that incidents were not incorrectly dismissed as benign.

Required Evidence: Quality Assurance (QA) logs or meeting minutes from SOC “Shift Handover” or weekly security reviews.

Pass/Fail Test: If there is no evidence of a “Second Look” or QA process for events closed at the first line, mark as Non-Compliant.

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