Annex A 5.26: Response to Information Security Incidents

Annex A 5.26 requires you to respond to information security incidents through a defined, repeatable process that triages, contains, investigates, communicates, and learns from incidents so they are handled consistently and evidence is retained for assurance. To operationalize it quickly, implement an incident response (IR) playbook, roles, logging, communications rules, and a closed-loop post-incident review with tracked corrective actions (ISO/IEC 27001 overview; ISMS.online Annex A control index).

Key takeaways:

• You need a documented, exercised incident response process with clear roles, decision rights, and escalation paths (ISO/IEC 27001 overview; ISMS.online Annex A control index).
• Auditors look for proof of operation: tickets, timelines, approvals, communications, lessons learned, and corrective actions tied to incidents.
• The most common failure is “policy-only IR” with no consistent triage, containment, or post-incident follow-through.

Annex a 5.26: response to information security incidents requirement is where your ISO 27001 program stops being theoretical and becomes operational. A well-written IR policy is not enough. You need a repeatable workflow that someone can run at 2 a.m., plus the records to prove it ran the way you said it would.

For a Compliance Officer, CCO, or GRC lead, the fastest path is to treat 5.26 as a control you can “show” in an audit: a defined process, trained responders, and incident records that demonstrate triage, containment, investigation, communication, and improvement. The control also sits at the junction of security operations, legal/privacy, IT operations, and third parties. That means your biggest implementation risks are usually ownership gaps, unclear escalation criteria, and missing evidence.

This page gives requirement-level guidance you can execute: who must be involved, what to build, what artifacts to retain, and how to avoid common audit failures. It also frames how to map 5.26 to ongoing control operation and recurring evidence capture so you stay assessment-ready (ISO/IEC 27001 overview; ISMS.online Annex A control index).

Regulatory text

Framework reference: ISO/IEC 27001:2022 Annex A 5.26 (ISO/IEC 27001 overview; ISMS.online Annex A control index)

Provided excerpt (summary-level): “ISO/IEC 27001:2022 Annex A control 5.26 implementation expectation (Response to Information Security Incidents).” (ISO/IEC 27001 overview; ISMS.online Annex A control index)

What the operator must do:
You must be able to demonstrate that your organization responds to information security incidents in a consistent, controlled way. In practice, that means you define the process (who does what, when), run it for real incidents and near-misses, capture evidence (tickets, logs, decisions), and improve the process based on outcomes (ISO/IEC 27001 overview; ISMS.online Annex A control index).

Plain-English interpretation

5.26 expects “muscle memory.” When an incident happens, your team should not invent the response. They should follow a known workflow that:

• identifies and triages the event,
• contains impact,
• investigates and documents what happened,
• communicates appropriately (internal and external as needed),
• closes with lessons learned and corrective actions.

The control is satisfied when you can show both design (documented playbooks, roles, rules) and operation (records of real incident handling plus improvements). A frequent assessor concern is “show me the last few incidents and walk me end-to-end.”

Who it applies to

Entity scope: Organizations implementing ISO/IEC 27001, especially service organizations with customer-facing systems and shared responsibility models (ISO/IEC 27001 overview; ISMS.online Annex A control index).

Operational context (where 5.26 becomes real):

• Central security operations (SOC or on-call security)
• IT operations (identity, endpoint, network, cloud)
• Engineering (app incidents, vulnerability response, hotfixes)
• Legal/privacy (potential breach assessment, regulator/customer notices)
• HR (insider events, acceptable use violations)
• Third parties (MSSP, cloud providers, SaaS, incident forensics firms, critical suppliers)

If you outsource monitoring or response, 5.26 still applies. You must govern the third party’s role, decision rights, and evidence delivery so you can prove your own control operation.

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

Use this sequence to operationalize fast and make it auditable.

1) Define “incident” and “security event” in your environment

• Write a short classification guide: event vs. incident vs. major incident.
• Include concrete triggers: confirmed malware, unauthorized access, credential compromise, data exposure, DoS affecting availability, lost device with sensitive data, misconfiguration exposing internal services.
• Define severity criteria (impact, scope, sensitivity, system criticality) so triage is repeatable.

Evidence: classification matrix; severity rubric; examples embedded in the runbook.

2) Assign roles, decision rights, and escalation paths

Document, at minimum:

• Incident Commander (authority to direct actions)
• Technical leads (identity, infrastructure, application)
• Communications lead (internal status updates, customer messaging coordination)
• Legal/privacy escalation point (when potential regulated data is involved)
• Third-party coordinator (if suppliers must engage)

Include an on-call model and backups. If you’re small, one person can hold multiple roles, but the roles must still exist on paper.

Evidence: RACI; on-call roster; escalation flowchart; named owners.

3) Build an incident response playbook that matches how you work

Keep it operational, not academic. Minimum sections:

• Intake channels (SIEM alert, helpdesk, customer report, third-party notice)
• Triage steps (validate, scope, severity assign)
• Containment actions (isolate host, revoke tokens, disable account, block IP, rotate keys)
• Investigation standards (what logs to pull, where to store, chain-of-custody expectations)
• Eradication and recovery (patch, rebuild, restore, validation checks)
• Communication rules (who can talk externally, approval steps, customer commitments)
• Closure requirements (root cause, corrective actions, tracking)

Implementation note: Map 5.26 to documented control operation and recurring evidence capture so you can prove it runs continuously, not just during audits (ISO/IEC 27001 overview; ISMS.online Annex A control index).

Evidence: IR policy/standard; playbooks; major incident checklist; communications templates.

4) Stand up the case management and logging backbone

Pick a single system of record (ticketing or IR platform). Require:

• unique incident ID,
• timestamps (detected, triaged, contained, recovered, closed),
• severity,
• systems/users affected,
• decisions and approvals,
• attached evidence (alerts, screenshots, logs, forensic notes),
• links to problem management / corrective actions.

Also define where forensic artifacts live and who can access them.

Evidence: incident tickets; audit trail exports; access control list for IR repository.

5) Create an internal/external communications protocol

You need rules for:

• internal stakeholder updates (executives, IT, customer support),
• customer notifications (who drafts, who approves),
• third-party notifications (cloud provider support, MSSP escalation),
• law enforcement engagement (if your organization uses it),
• evidence-preserving communications (avoid contaminating facts).

Do not overcomplicate: a one-page comms SOP plus templates is enough if it is followed.

Evidence: comms SOP; distribution lists; approved templates; sample redacted incident update.

6) Run tabletop exercises and convert outcomes into actions

Tabletops prove readiness and expose gaps in tooling, authority, and communications. Focus on a few realistic scenarios (credential compromise, ransomware, exposed cloud storage, third-party breach notification affecting you). Capture issues as tracked actions with owners.

Evidence: tabletop agenda; attendee list; after-action report; action register with status.

7) Close the loop with post-incident review and corrective action tracking

Define a consistent closure standard:

• root cause (technical and process),
• control failures (logging gaps, delayed escalation, missing MFA, weak vendor notification),
• corrective actions with due dates and owners,
• validation of fixes (tests, config snapshots, control evidence).

This is where audit teams separate mature programs from “response-only” teams.

Evidence: post-incident report; corrective action tickets; change records; validation evidence.

Required evidence and artifacts to retain

Keep these artifacts in a single audit-ready folder structure (or GRC system) with access controls:

Artifact	What it proves	Good-enough content
IR policy/standard + playbooks	Defined process	Roles, phases, escalation, comms
Incident register	Consistent operation	List of incidents, severity, dates, status
Incident tickets/case files	Execution evidence	Timeline, actions, approvals, attachments
Forensic/log extracts (redacted where needed)	Investigation quality	What was reviewed and why
Communications records	Controlled messaging	Internal updates, customer drafts/approvals
Post-incident reports	Learning loop	Root cause + corrective actions
Corrective action tracker	Follow-through	Owner, status, validation notes
Tabletop/exercise records	Readiness	Findings and actions

Common exam/audit questions and hangups

Expect these and prepare your evidence path:

• “Show me your incident criteria. How do you decide severity?”
• “Walk me through your last incident end-to-end. Where is the timeline captured?”
• “Who can declare a major incident? Who approves customer communications?”
• “How do you ensure third parties notify you and cooperate during incidents?”
• “Where are lessons learned documented, and how do you verify corrective actions are completed?”
• “How do you handle incidents that involve personal data or regulated data types?”
  A common hangup: the team can explain verbally, but the ticket lacks timestamps, decision notes, and closure evidence.

Frequent implementation mistakes and how to avoid them

1. Policy-only IR with no case records.
   Fix: require every incident to have an ID and a ticket with minimum fields before closure.

2. Unclear authority during incidents.
   Fix: name the Incident Commander role and decision rights; document who can take disruptive containment actions.

3. No linkage between incidents and corrective actions.
   Fix: require a post-incident review for defined severities and link actions to change management.

4. Third-party blind spots.
   Fix: contractually require incident notification and cooperation; operationally test contact paths and evidence handoff during tabletops.

5. Over-classifying everything as “low” to reduce work.
   Fix: define severity criteria tied to impact and data/system criticality; have periodic management review of incident categorization patterns.

Enforcement context and risk implications

No public enforcement cases were provided in the source catalog for this control, so this page does not cite specific actions. Practically, weak incident response increases the likelihood of extended outages, uncontrolled data exposure, inconsistent customer communications, and audit findings that can delay ISO 27001 certification or surveillance outcomes (ISO/IEC 27001 overview; ISMS.online Annex A control index).

A practical 30/60/90-day execution plan

First 30 days (stabilize the minimum viable IR capability)

• Appoint IR owner and Incident Commander role; publish escalation contacts.
• Draft/refresh IR policy + one primary playbook aligned to your tech stack.
• Stand up the incident register and ticket minimum fields.
• Define incident classification and severity rubric.
• Identify log sources required for investigations and confirm access paths.

Next 60 days (prove operation and tighten interfaces)

• Run at least one tabletop and track findings to closure.
• Formalize comms SOP and templates; align with legal/privacy review path.
• Add third-party incident touchpoints: who to call, what evidence to request, how to document.
• Create a post-incident review template and require it for higher-severity incidents.

By 90 days (make it audit-ready and repeatable)

• Demonstrate a consistent evidence trail across incidents (tickets, timelines, attachments).
• Review incident trends and validate corrective actions through testing or configuration checks.
• Train responders and cross-functional stakeholders on their roles.
• Build a recurring evidence capture routine so 5.26 can be assessed without scrambling (ISO/IEC 27001 overview; ISMS.online Annex A control index).
• If you use Daydream, map 5.26 to your control library, attach the playbooks and templates, and schedule recurring evidence requests so incident records and post-incident actions stay continuously organized for audits.

Frequently Asked Questions

Does Annex A 5.26 require a formal “SOC”?

No. It requires an effective response capability with defined roles, process, and evidence. A small organization can meet the requirement with an on-call model if responsibilities, escalation, and records are clear (ISO/IEC 27001 overview; ISMS.online Annex A control index).

If our MSSP handles incidents, are we covered?

Only if you can show governance and evidence. Your contracts and operating procedures should define notification timelines, cooperation, and what case artifacts the MSSP provides so you can demonstrate control operation (ISO/IEC 27001 overview; ISMS.online Annex A control index).

What evidence is most persuasive to an ISO 27001 auditor for 5.26?

Incident tickets with a clear timeline, containment actions, investigation notes, and closure with lessons learned and corrective actions. Tabletop records help, but auditors usually want to see real incident handling evidence.

How do we handle “near misses” and still keep the workload manageable?

Track near misses as security events with lightweight documentation, then promote to incidents when predefined criteria are met. Keep the criteria short and enforce the ticket minimum fields so classification stays consistent.

Do we need to notify customers for every security incident?

Annex A 5.26 focuses on response capability, not specific notification laws. Set internal rules for when customer communications are drafted and approved, and route potential regulated-data situations to legal/privacy for determination.

How do we avoid storing sensitive forensic data in our ticketing system?

Store bulky or sensitive artifacts in a controlled evidence repository and link it from the incident ticket. Keep access limited and document who can view or export artifacts as part of your IR procedure.