Assessment and Decision on Information Security Events
Plain English Translation
ISO 27001 Annex A.5.25 requires organizations to have a structured process for evaluating security alerts and events to determine if they qualify as actual information security incidents. Not every event (like a failed login or a port scan) is an incident; incident triage ensures that real threats are escalated according to their severity and potential impact. This control formally defines the criteria used to filter, classify, and escalate events to the incident response team, ensuring swift action while preventing alert fatigue.
Technical Implementation
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Required Actions (startup)
- Define basic criteria for what constitutes a security incident versus a normal event in the Incident Response Plan.
- Manually review alerts from key infrastructure (like basic EDR or cloud native alerts) to decide if escalation is required.
Required Actions (scaleup)
- Implement a centralized alerting tool with tuned rules to reduce false positives.
- Document an incident severity classification matrix (e.g., Sev1 to Sev4) to guide escalation based on asset criticality and impact.
Required Actions (enterprise)
- Deploy a SIEM/SOAR platform to automatically triage and assess low-level events.
- Run a 24/7 Security Operations Center (SOC) with structured playbooks and automated escalation to the incident response team for high-fidelity alerts.
An event is an identified occurrence of a system, service, or network state indicating a possible breach or failure of controls, whereas an incident is a single or series of unwanted events that have a significant probability of compromising business operations and threatening information security.
You assess a security alert using predefined criteria such as the potential impact on confidentiality, integrity, and availability (CIA), the reliability of the source, and whether the event bypasses existing security controls. For consistent triage, teams often need accurate asset criticality and ownership context; tools like WatchDog Security's Asset Inventory can centralize that information so analysts apply criteria quickly and consistently.
It requires an organization to formally assess information security events (like alerts from monitoring systems) and make a structured decision on whether they must be categorized and treated as information security incidents.
Criteria should include the type of threat (e.g., malware, unauthorized access), the criticality of the affected assets, the scope of the impact (e.g., single endpoint vs. whole network), and the potential legal or regulatory consequences.
You create a matrix by plotting the potential impact of an incident (low to critical) against its urgency or likelihood, assigning each combination a severity level (e.g., SEV-1 to SEV-4) that dictates the required response time and resources. To keep it auditable, document the decision rules and review cadence; tools like WatchDog Security's Risk Register can store the matrix assumptions and link severity to business impact reporting.
Auditors typically look for an Incident Response Plan outlining the triage process, alongside evidence such as incident tickets, SOC triage logs, or root cause analysis reports showing how an event was assessed and classified. WatchDog Security's Compliance Center can map these records to A.5.25, track collection status, and maintain an audit trail of who provided what evidence. When sharing sensitive logs with auditors or stakeholders, WatchDog Security's Secure File Sharing can provide encrypted delivery, TOTP verification, and access logs.
While ISO 27001 doesn't specify exact times, triage and escalation should happen in a timely manner based on the organization's risk appetite and SLA commitments, often within minutes or hours for high-fidelity alerts.
Triggers include confirmed data exfiltration, compromise of privileged accounts, successful malware execution on critical servers, or events that breach predefined risk thresholds indicating a high severity incident.
Yes, Security Information and Event Management (SIEM) and Security Orchestration, Automation, and Response (SOAR) tools are highly recommended to automate the initial assessment, filter false positives, and escalate genuine incidents. Even when triage is automated, WatchDog Security's Compliance Center can capture the supporting artifacts and demonstrate that decision criteria were consistently applied for ISO 27001 audits.
A.5.24 covers the preparation (policies and roles), A.5.25 is the triage phase (deciding if an event is a real incident), and A.5.26 governs the actual response and containment actions taken once an incident is declared.
Auditors want to see that analysts use defined criteria, follow a repeatable process, and record decisions (including why an event was or wasn’t declared an incident). WatchDog Security's Compliance Center can map triage procedures and supporting artifacts (tickets, logs, playbooks, approvals) to ISO 27001 A.5.25, track evidence collection status, and preserve an audit trail of decision records over time.
Severity should reflect what was affected (critical systems, privileged identities, regulated data) and who else may be impacted (key vendors or shared services). WatchDog Security's Asset Inventory can help maintain current asset ownership and criticality context, while WatchDog Security's Vendor Risk Management can help identify high-impact third parties so triage criteria and escalation thresholds reflect real business exposure.
| Version | Date | Author | Description |
|---|---|---|---|
| 1.0.0 | 2026-02-17 | WatchDog Security GRC Team | Initial publication |
