Annex A 5.25: Assessment and Decision on Information Security Events

Annex A 5.25 sits in the “Organizational controls” set in ISO/IEC 27001:2022 and focuses on the moment where uncertainty becomes operational risk: the point at which a signal (alert, user report, third-party notice) must be assessed and turned into a decision. If your team cannot show a consistent method for evaluating events and deciding next steps, auditors typically conclude your incident management is ad hoc, even if engineers respond quickly in practice. ¹

For a Compliance Officer, CCO, or GRC lead, the fastest path is to treat 5.25 as a control over decision quality and traceability. You are building: (1) a shared definition of an “information security event,” (2) a minimum assessment standard (what facts must be gathered before deciding), (3) clear decision authority and escalation thresholds, and (4) durable records that prove the process ran. This page gives requirement-level implementation guidance you can hand to security operations, IT, and business owners and then audit without guesswork. ²

Regulatory text

Provided excerpt (summary): “ISO/IEC 27001:2022 Annex A control 5.25 implementation expectation (Assessment and Decision on Information Security Events).” ²

Operator interpretation (what you must do):

• Assess information security events consistently (not incident-only). Capture enough facts to judge severity, scope, and business impact.
• Make and document decisions for each event: close as benign, monitor, initiate response tasks, or escalate to a formal information security incident process.
• Demonstrate repeatability: the same class of event should lead to comparable decisions, unless documented context explains the difference. ¹

Plain-English interpretation

You need a reliable “triage and decision” layer between raw signals and full incident response. Every event should leave a trail that answers: What happened? How did we assess it? Who decided? What did we do next? ¹

If you already have incident response, 5.25 fills the gap that auditors often probe: the period before you declare an incident, including false positives, near misses, and low-severity events that still require tracking and learning.

Who it applies to

Entities

Any organization running an ISMS aligned to ISO/IEC 27001, including service organizations that must demonstrate controlled operations to customers and auditors. ²

Operational context (where it shows up)

• Security monitoring and alerting (SIEM/EDR/cloud alerts)
• Helpdesk tickets and end-user reports (phishing, lost devices)
• Third-party notifications (supplier compromise, exposed credentials)
• Abuse reports (credential stuffing, fraud signals)
• Change-related anomalies (misconfigurations, unexpected access)

If your business has multiple intake paths (ITSM, SOC tooling, email inboxes), 5.25 requires you to unify assessment and decision standards even if tooling differs.

What you actually need to do (step-by-step)

1) Define “information security event” and “incident” in your context

Create a short standard that:

• Defines an event as a detected or reported occurrence relevant to information security (including suspected issues and false alarms).
• Defines an incident as an event (or series of events) that meets escalation thresholds requiring formal incident handling. ¹

Practical tip: Put these definitions directly into your IR policy/standard and your triage playbook. Auditors look for consistency across documents.

2) Establish a single intake register (even if you have multiple sources)

You need one system of record where each event gets:

• Unique identifier
• Timestamp (opened/updated/closed)
• Source (tool, person, third party)
• Affected asset/service (link to asset inventory or service catalog)
• Initial categorization (phishing, malware, access anomaly, data exposure, etc.)

This can be an IR ticket queue, ITSM, or a case management tool. The key is that events are trackable end-to-end.

3) Create a minimum assessment checklist (“triage standard”)

For each event type, require a baseline set of facts before disposition:

• Scope: systems, identities, data types potentially affected
• Credibility: evidence quality (alert fidelity, corroborating logs)
• Impact lens: confidentiality/integrity/availability, customer impact, regulatory trigger potential
• Containment need: whether immediate actions are required before full investigation
• Uncertainty notes: what you do not know yet and how you will find out

Make the checklist short enough that operators will actually complete it, but strict enough that decisions are defensible.

4) Implement a decision matrix with clear dispositions

Define allowed outcomes, for example:

• Close as benign (document rationale and evidence)
• Monitor (set follow-up owner and next check)
• Respond as event (assign tasks, track remediation without “incident” declaration)
• Escalate to incident (invoke incident process, communications, and potentially legal/privacy)

Build escalation thresholds that reflect your risk appetite and obligations. Keep it practical: “customer data potentially exposed” or “privileged access suspected” are easier to run than abstract severity scores.

5) Assign decision authority and escalation rules

Document who can:

• Close events
• Escalate to incident
• Approve customer notifications or regulator-facing steps (often outside 5.25, but the decision trail starts here)

Common operating model:

• SOC/IT can triage and recommend disposition.
• Incident Commander (or Security Manager) approves escalation to incident.
• Legal/Privacy/CCO approves external notifications where required.

6) Train and test with tabletop-style triage drills

Run short drills focused on event assessment and the decision record:

• Use real examples: suspicious login, malware alert, third-party breach notice.
• Validate that two different analysts reach the same disposition using the matrix.
• Confirm the ticket contains the required fields and attachments.

7) Operationalize recurring evidence capture (auditor-ready)

Turn evidence into a routine:

• Weekly or monthly export of event log metadata (counts are fine, but focus on completeness and traceability rather than stats).
• Sample-based QA review of closed events for documentation quality.
• Trend review to feed corrective actions (links to continual improvement). ²

Where Daydream fits naturally: Daydream can map Annex A 5.25 to your documented workflow, then prompt recurring evidence capture (samples, decision logs, and approvals) so you are not assembling proof during audit season.

Required evidence and artifacts to retain

Keep artifacts that prove both design and operation:

Control design artifacts

• Event/incident definitions and triage standard (policy or standard)
• Decision matrix / escalation criteria document
• RACI or role definitions for triage, escalation, and approvals
• Tooling/workflow diagram showing intake-to-decision path (even a one-page schematic)

Operating evidence artifacts

• Event register export (ticket IDs, timestamps, dispositions, owners)
• Completed triage checklists (embedded in tickets or attached)
• Decision approvals (comments, approvals in ticketing system, incident declaration record)
• Supporting evidence (logs, screenshots, third-party notice, email headers)
• QA review records and corrective actions (where triage quality issues were found)

Retention note: Use your internal retention standard; auditors mainly test that you can produce records for a representative period and that records are tamper-resistant.

Common exam/audit questions and hangups

Auditors commonly probe:

1. “Show me how you decide an event becomes an incident.” Expect to walk through your matrix and show examples across categories.
2. “How do you ensure completeness of event capture?” They will ask about inboxes, Teams/Slack reports, and tool alerts that bypass the register.
3. “Who has authority to close high-risk events?” If junior staff can close anything without oversight, expect findings.
4. “Prove this works in practice.” You will need real tickets with assessment details, not just a policy. ¹

Frequent implementation mistakes and how to avoid them

Mistake	Why it fails in audits	Fix
Treating all events as incidents	Inflates noise and weakens decision discipline	Keep “event” as the default; escalate by threshold
No written criteria for escalation	Decisions look subjective	Publish a matrix and require rationale in tickets
Decisions made in chat, not in the case record	No audit trail	Require case notes and approvals in the system of record
“Closed” with no evidence	Cannot defend disposition	Minimum evidence checklist per event type
Multiple intake paths with no reconciliation	Events fall through cracks	Central register and periodic reconciliation

Enforcement context and risk implications

ISO/IEC 27001 is a certifiable standard, not a regulator. Your “enforcement” is typically through:

• Certification audit nonconformities
• Customer security reviews and contract obligations
• Incident-related disputes where documentation is scrutinized (for example, whether you acted reasonably based on what you knew)

Risk outcomes when 5.25 is weak:

• Late escalation to incident response, increasing impact
• Inconsistent decision-making across teams and time zones
• Poor defensibility during customer audits because you cannot show how you assessed and decided ²

Practical 30/60/90-day execution plan

First 30 days (stabilize triage and decision records)

• Inventory all event sources (SIEM, EDR, cloud, helpdesk, third-party emails).
• Pick the system of record for the event register and enforce mandatory fields.
• Draft the event/incident definitions and a first-pass decision matrix.
• Start capturing evidence on every event going forward (even if criteria are still evolving).

Days 30–60 (standardize and QA)

• Publish the triage checklist by event type (phishing, endpoint, access anomaly, third-party notice).
• Implement approval rules for high-risk dispositions (for example, escalation-required categories).
• Train analysts, IT, and helpdesk on intake and documentation standards.
• Begin sample-based QA review and document corrective actions.

Days 60–90 (prove repeatability and audit readiness)

• Run triage drills and document outcomes and improvements.
• Tune decision thresholds based on false positives and missed escalations.
• Create an audit packet: policy/standard, matrix, RACI, workflow diagram, and a curated sample set of event records showing each disposition path.
• If you use Daydream, configure control mapping and recurring evidence tasks so the audit packet stays current.

Frequently Asked Questions

Do we need a SOC to meet annex a 5.25: assessment and decision on information security events requirement?

No. You need a consistent assessment-and-decision process with clear ownership and auditable records. A helpdesk-led model can work if escalation criteria and approvals are defined and followed. ¹

How do we distinguish an “event” from an “incident” without overcomplicating it?

Define an event as any security-relevant signal, then define an incident as an event that crosses explicit thresholds (data exposure suspected, privileged access abuse, or service disruption). Keep the thresholds written and require rationale in the case record. ¹

Can we manage events in our ITSM tool instead of a dedicated IR platform?

Yes, if the ITSM workflow can capture required fields, preserve evidence, and show approvals and timestamps. Auditors care about traceability and repeatability more than tool branding. ²

What evidence do auditors usually request first?

They typically ask for the event register, then a sample of event tickets showing assessment details and the documented decision to close, monitor, respond, or escalate. They also ask for the written decision criteria and roles. ¹

How do we handle third-party notifications under 5.25?

Treat third-party notices as event intake sources, create a case, assess credibility and relevance to your environment, and document the disposition and follow-up tasks. Link the notice and your assessment notes to the event record. ²

What’s the simplest way to show this control “operates” over time?

Maintain a continuous event log with complete fields, keep representative samples with evidence attachments, and document periodic QA review outcomes. Daydream can automate recurring evidence capture so you do not rebuild proof for each audit. ²

Footnotes

1. ISMS.online Annex A control index

2. ISO/IEC 27001 overview