Security incidents are inevitable. What defines a resilient organisation is not just how it responds, but how it learns. A post-incident review (PIR) is a structured process to analyse what happened, why it happened, and how to prevent recurrence. Done well, it transforms a crisis into a catalyst for improvement.
Why Post-Incident Reviews Matter
According to NIST and ISO 27001, PIRs are essential for:
- Continuous improvement of security controls and incident response plans.
- Root cause analysis to identify technical, procedural, or human failures.
- Compliance with standards like ISO 27001 Annex A 5.26 and NIST SP 800-61r3
- Organisational learning that strengthens resilience and reduces future risk
Step-by-Step Guide to Conducting a PIR
1. Initiate the Review Promptly
Conduct the review while details are fresh. This ensures accuracy and urgency, helping teams reconstruct the incident timeline effectively
2. Rebuild the Incident Timeline
Document the sequence of events from detection to resolution. Include timestamps, decisions made, and tools used. This helps identify delays, missteps, and successful interventions.
3. Perform Root Cause Analysis
Use structured techniques (e.g., 5 Whys, Fishbone diagrams) to uncover the underlying causes—whether technical misconfigurations, process gaps, or human error
4. Assess Team Performance
Evaluate how the incident response team performed against documented procedures. Identify gaps in training, communication, and escalation protocols
5. Analyse Business Impact
Quantify financial, operational, legal, and reputational impacts. Include both direct costs and indirect consequences such as client churn or regulatory scrutiny
6. Capture Context
Understand the environment in which decisions were made. Document constraints, assumptions, and evolving threat intelligence during the incident
7. Engage Cross-Functional Stakeholders
Include IT, security, legal, compliance, HR, and business owners. Their perspectives enrich the review and ensure that lessons are shared beyond the security team
8. Focus on Structural Learning
Avoid blame. Instead, ask whether teams were equipped to make good decisions. Use findings to improve documentation, tooling, and funding
9. Document and Share Findings
Create a formal report with:
- Executive summary
- Timeline
- Root cause analysis
- Impact assessment
- Recommendations
- Action plan
Ensure it’s reviewed by senior leadership and integrated into ISMS documentation
10. Track Remediation and Improvements
Assign owners to each action item. Use internal audit and compliance reviews to verify implementation. Update incident response plans and training materials according
Standards Alignment
ISO 27001 Annex A 5.26
Requires organisations to respond to information security incidents and take corrective actions. PIRs are a key mechanism for fulfilling this clause
NIST SP 800-61r3
Outlines four phases: Preparation, Detection & Analysis, Containment/Eradication/Recovery, and Post-Incident Activity. PIRs fall under the final phase and are critical for feedback loops
A well-executed post-incident review is not just a compliance checkbox—it’s a strategic tool. It helps organisations, especially in regulated sectors, evolve from reactive defence to proactive resilience.
