ISO/IEC 27001:2022 Annex A · Control 5.26

Response to Information Security Incidents: A Practical Implementation Guide

Contain harm, restore trusted operations and coordinate decisions through a disciplined response process.

This control addresses responding to information security incidents according to established procedures.

Practical interpretation: Fast action matters, but uncontrolled action can destroy evidence or increase impact. Response should balance containment, investigation, recovery, legal duties and business continuity.

What should the control achieve?

Incidents have accountable command and objectives.
Containment and eradication actions are authorized.
Evidence and decisions are preserved.
Recovery is verified before closure.

Step-by-step implementation

Activate command

Confirm severity, Incident Manager, objectives and communication channel.

Analyze scope

Build timeline, affected assets, identities, data and business impact.

Contain safely

Select immediate and longer-term measures with owners and rollback plans.

Eradicate causes

Remove persistence, vulnerabilities, compromised credentials and unsafe configurations.

Recover and monitor

Restore from trusted state, validate controls and watch for recurrence.

Communicate and close

Meet stakeholder duties, document decisions and approve closure.

What this could look like in practice

During ransomware, the Incident Manager isolates affected segments, preserves forensic images, invokes continuity plans and coordinates Legal, Communications and external responders. Systems return only after clean rebuild and validation.

Activity	Practical implementation	Evidence
Command	Named manager sets priorities and records decisions.	Incident log
Containment	Technical actions are approved and timestamped.	Action timeline
Recovery	Business and technical owners verify trusted operation.	Recovery acceptance
Communication	Notifications use approved facts and channels.	Communication record

Implementation evidence

Incident records
Decision timeline
Containment approvals
Forensic evidence
Communication logs
Recovery validation
Risk acceptance
Closure approval

Useful metrics

Time to contain
Time to recover critical service
Repeated containment failures
Incidents with complete timelines

Common mistakes

Allowing multiple uncoordinated commanders.
Rebuilding before preserving evidence.
Communicating speculation.
Restoring without removing root cause.
Closing when service returns but actions remain.

Questions an auditor may ask

Who commanded the last incident?
How were containment decisions authorized?
Show evidence of trusted recovery.
How were stakeholders informed?

Implementation test: Trace a recent incident from declaration through containment, eradication, recovery, communication and formal closure.

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This independent educational guide paraphrases the practical intent of the control and does not replace the official ISO standards, professional advice or an organization-specific risk assessment. It is not affiliated with or endorsed by ISO.

ISO 27001 Annex A 5.26: Response to Information Security Incidents – Practical Implementation Guide