In this ultimate how to implement 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:
- The requirement of the control
- The required implementation steps
- The minimum requirement
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
- ISO 27001 Annex A 5.25 Assessment and Decision on Information Security Events Implementation Checklist
- 1. Define the Manual Event Logging Baseline
- 2. Assign a Human ‘Triage Lead’
- 3. Implement a Manual Event-to-Incident Classification Matrix
- 4. Configure Out-of-Band Event Alerts
- 5. Establish a Physical Evidence Log of Assessments
- 6. Perform Manual Log Correlation Dry Runs
- 7. Define ‘False Positive’ Thresholds
- 8. Implement a ‘Second Opinion’ Protocol for High-Impact Events
- 9. Conduct Technical Peer Review of Automated Filters
- 10. Store Triage Evidence Offline
- ISO 27001 Annex A 5.25 SaaS / GRC Platform Implementation Failure Checklist
Implementing ISO 27001 Annex A 5.25 is the governance process of evaluating potential security incidents through manual log analysis. The primary implementation requirement centers on human-led triage and classification matrices, providing the business benefit of accurate threat detection and high-integrity evidence for audit trails.
ISO 27001 Annex A 5.25 Assessment and Decision on Information Security Events Implementation Checklist
Use this implementation checklist to achieve compliance with ISO 27001 Annex A 5.25. Real-world security is verified through the manual interrogation of raw system logs and human decision-making, not by relying on the ‘auto-remediation’ promises of a GRC dashboard.
1. Define the Manual Event Logging Baseline
Control Requirement: Establish a clear baseline of what constitutes an information security event across all organisational assets.
Required Implementation Step: Log into your primary domain controller and firewall. Manually document the specific Event IDs (e.g., Windows Event ID 4625 for failed logins) that must be captured, ensuring you aren’t just trusting a default ‘collect all’ setting that creates noise.
Minimum Requirement: A documented list of high-priority Event IDs and log sources specific to your local infrastructure.
2. Assign a Human ‘Triage Lead’
Control Requirement: Appoint a competent individual or team to assess events and determine if they should be classified as incidents.
Required Implementation Step: Designate a lead engineer as the primary ‘Triage Lead’. Update their physical job description to include the manual review of daily event summaries, ensuring accountability lies with a person, not an algorithm.
Minimum Requirement: A signed appointment letter or updated roles-and-responsibilities matrix for the Triage Lead.
3. Implement a Manual Event-to-Incident Classification Matrix
Control Requirement: Develop a criteria-based assessment process to decide if an event is a security incident.
Required Implementation Step: Create a physical or local spreadsheet matrix. Define specific thresholds—such as “5 failed login attempts from a foreign IP within 10 minutes”—that mandate an escalation from ‘Event’ to ‘Incident’.
Minimum Requirement: A 1-page decision matrix used by IT staff to categorise events during the triage process.
