Assessment and Decision on Information Security Events – ISO 27001 A.5.25

Introduction

The Assessment and Decision on Information Security Events control (ISO 27001:2022 Clause A.5.25) ensures that all detected security events are systematically evaluated, classified, and escalated where necessary.

Not every alert is an incident — but failing to properly assess events leads to:

• Missed security incidents
• Delayed response
• Alert fatigue in SOC teams
• Ineffective incident management

This control establishes a structured decision-making layer between event detection and incident response.

What This Control Is About (Basic Information)

Comply Agent shows:

• Title: Assessment and decision on information security events
• Control ID: UC-IN-025
• Category: Incident Response
• Subcategory: Event Management
• Version: v1.0

Description

Implement security event monitoring, incident classification criteria, and decision procedures to assess information security events and determine if they constitute information security incidents. This includes defining thresholds for escalation and clear roles and responsibilities for event analysis and decision-making.

Objective

To ensure timely and effective assessment of security events to differentiate them from actual information security incidents, enabling appropriate response actions.

Implementation & Guidance

Comply Agent structures this control as a SOC-driven decision framework:

1. Define Event Classification Criteria

Organizations must define:

• Event severity levels (Low / Medium / High / Critical)
• Criteria for incident declaration
• Impact and likelihood thresholds

2. Establish Event Monitoring and Intake

• Integrate logs from:
  • SIEM
  • EDR
  • Firewalls and IDS/IPS
• Normalize and centralize event data

3. Implement Event Assessment Workflow

Comply Agent highlights:

• Triage each event
• Perform initial analysis
• Determine:
  • False positive
  • Security event
  • Confirmed incident

4. Define Escalation and Decision Paths

• Establish escalation thresholds
• Define when SOC escalates to:
  • Incident Response Team
  • Management

5. Assign Roles and Responsibilities

• SOC Analysts → Initial triage
• Security Leads → Incident decision
• Management → Critical escalation

6. Maintain Event Assessment Records

• Log all decisions
• Record justification
• Track incident declaration history

Evidence Examples

Comply Agent shows:

• Incident response plan with defined event classification and incident declaration procedures
• Records of security event assessments and incident decisions
• Training materials and attendance logs for incident response personnel

Operational Details

Comply Agent shows:

• Frequency: Continuous
• Review Cycle: Continuous
• Owner Role: Security Operations Center (SOC) Team
• Responsible Role: Security Operations Center (SOC) Team
• Automation Score: 75%
• Last Updated: As per system records

Interpretation

• High automation (75%) typically includes:
  • SIEM correlation rules
  • Automated alert triage
  • SOAR-based workflows

Compliance & Risk Management

Comply Agent shows:

• Status: Not Started
• Compliance Status: N/A
• Control Type: Administrative
• Maturity Level: Level 3
• Risk Domain: Operational Resilience
• Clause Reference: ISO 27001:2022 A.5.25

Key Risks Addressed

• Misclassification of security events
• Delayed incident response
• Alert fatigue and missed critical threats
• Lack of traceability in incident decisions

Framework Mappings

Comply Agent shows strong cross-framework alignment:

1. Primary Mapping

• ISO 27001:2022 – A.5.25 (Exact)

2. Supporting Controls

• SOC 2
  • CC7.2 – Monitoring and detection of security events

3. Extended Mappings

• DORA
  • Article 10 – ICT incident management
  • Article 11 – Incident reporting
• GDPR
  • Article 32 – Security of processing
  • Article 33 – Breach notification
• NIST CSF
  • DE.AE-2 – Event analysis
  • DE.CM-1 – Continuous monitoring
  • RS.AN-1 – Incident analysis

Evidence Library

Comply Agent shows the required audit evidence:

1. Security Event Logs (Auto-collected)

Logs from SIEM, EDR, and other security tools showing event occurrences and initial analysis.

2. Incident Classification Procedures

Documented procedures outlining classification criteria, severity levels, and decision workflows.

3. Event Assessment Records (Auto-collected)

Records of assessed security events, decisions made, and justification for classification outcomes.

FAQs: Assessment and Decision on Information Security Events – ISO 27001 A.5.25

1. What is the difference between an event and an incident?

An event is any observable occurrence; an incident is a confirmed security breach or threat.

2. Who performs the assessment?

Comply Agent shows: SOC Team.

3. Why is this control critical?

Because incorrect classification leads to either:

• Overreaction (wasted effort)
• Underreaction (missed breaches)

4. What do auditors expect?

• Defined classification criteria
• Event-to-incident decision logs
• Evidence of escalation processes

5. Is automation required?

Highly recommended for:

• Log ingestion
• Event correlation
• Alert prioritization