What is ISO 27001 Annex A 5.27 – Learning from Information Security Incidents?
ISO 27001 Annex A 5.27 requires an organization to use knowledge gained from information security incidents to improve its information security controls, processes, and overall ISMS.
An organization should not treat an incident as finished simply because the immediate problem has been resolved.
The organization should ask:
- What happened?
- Why did it happen?
- What allowed it to happen?
- Which controls worked?
- Which controls failed or were missing?
- Could the incident happen again?
- What should we change?
- Does the risk assessment need to be updated?
- Do policies, procedures, training, or technical controls need improvement?
Simple explanation
An incident is not fully valuable until the organization learns from it and uses those lessons to reduce the chance or impact of another incident.
For example, if an employee’s account is compromised, simply resetting the password solves the immediate problem.
Learning from the incident means understanding why the account was compromised and what should change to prevent a similar incident from happening again.
Why is Annex A 5.27 Important?
Security incidents provide real-world information about weaknesses in an organization’s security environment.
Even organizations with policies, security tools, and risk assessments can experience incidents.
The important question is what the organization does after the incident.
Effective learning can help an organization:
- Identify weaknesses in existing controls
- Improve security policies and procedures
- Reduce recurring incidents
- Improve employee awareness
- Strengthen technical controls
- Improve incident-response procedures
- Update risk assessments
- Improve supplier management
- Improve monitoring and detection
- Improve business continuity and recovery
- Strengthen the ISMS
Simple principle
Don’t just fix the incident. Fix the weakness that allowed the incident to happen.
A.5.26 vs A.5.27 – What is the Difference?
These two controls are closely connected.
| Control | Main Purpose |
|---|---|
| A.5.24 | Prepare for information security incidents |
| A.5.25 | Assess security events and determine whether they are incidents |
| A.5.26 | Respond to information security incidents |
| A.5.27 | Learn from incidents and improve |
| A.5.28 | Collect and preserve evidence |
A simple way to understand the sequence is:
Prepare → Assess → Respond → Learn → Preserve Evidence
A.5.26 asks:
How do we respond to this incident?
A.5.27 asks:
What did we learn from this incident, and what should we improve?
What Does A.5.27 Require?
The organization should have a defined process for reviewing information security incidents and identifying lessons that can improve information security.
The review should consider both:
What went well?
For example:
- Alert was detected quickly
- Employee reported the phishing email
- Incident owner was clearly identified
- Account was disabled quickly
- Logs were available
- Communication process worked
What did not go well?
For example:
- MFA was not enabled
- Excessive access rights existed
- Logs were not retained
- Incident escalation was delayed
- Employees did not know how to report incidents
- Supplier response was slow
- Recovery procedures were incomplete
The organization should then convert these observations into improvement actions.
Activities Required to Implement A.5.27
1. Conduct a Post-Incident Review
After an incident has been contained and the organization has stabilized the situation, conduct a structured review.
The review should consider:
- Incident description
- Date and time
- Systems affected
- Information affected
- Business impact
- Root cause
- Contributing factors
- Controls that failed
- Controls that worked
- Response effectiveness
- Communication effectiveness
- Recovery effectiveness
- Lessons learned
- Corrective actions
Not every minor event requires a large investigation. The depth of the review should be proportionate to the severity and potential impact.
2. Establish an Incident Timeline
Create a timeline showing what happened.
Example:
| Time | Event |
|---|---|
| 09:12 | Employee receives phishing email |
| 09:18 | Employee clicks malicious link |
| 09:21 | Attacker successfully authenticates |
| 09:35 | Unusual login detected |
| 09:42 | Security team investigates |
| 09:50 | Account disabled |
| 10:05 | Sessions revoked |
| 11:30 | Logs reviewed |
| 14:00 | No evidence of data exfiltration identified |
| Next Day | Post-incident review initiated |
A timeline helps the organization identify where delays or control weaknesses occurred.
3. Identify the Root Cause
The organization should go beyond the immediate symptom.
For example:
Incident: Employee account compromised.
Immediate cause:
Employee entered credentials into a phishing website.
Possible contributing factors:
- Weak phishing awareness
- No phishing-resistant MFA
- Excessive account privileges
- Insufficient login monitoring
- No conditional access
- Inadequate alerting
The objective is not simply to identify who made the mistake.
The objective is to understand:
What conditions allowed the incident to occur or increase its impact?
4. Perform Root Cause Analysis
Organizations can use different techniques depending on the complexity of the incident.
Examples include:
5 Whys
Why was the account compromised?
→ Employee entered credentials into a phishing website.
Why did the employee enter credentials?
→ The phishing page looked legitimate.
Why was the attack not blocked?
→ Email filtering did not detect it.
Why was the account still vulnerable?
→ Strong MFA protection was not implemented.
Why had strong MFA not been implemented?
→ Identity security requirements had not been fully defined.
This can reveal a broader process or control weakness.
5. Evaluate Existing Controls
Ask whether existing controls worked as intended.
For example:
| Control | Expected | Actual | Lesson |
|---|---|---|---|
| MFA | Prevent unauthorized access | Bypass/weak method | Strengthen MFA |
| Email security | Detect phishing | Missed email | Improve filtering |
| Monitoring | Detect unusual login | Alert generated late | Improve detection |
| Access control | Limit damage | Excessive privileges | Reduce permissions |
| Incident response | Contain quickly | Worked as expected | Retain process |
This helps determine whether the organization needs:
- New controls
- Stronger controls
- Better configuration
- Better monitoring
- Better training
- Better procedures
6. Identify Corrective and Improvement Actions
Lessons learned should result in practical actions.
For example:
| Finding | Improvement Action | Owner | Due Date |
|---|---|---|---|
| MFA weakness | Implement stronger MFA | IT | 30 days |
| Excessive access | Review privileged access | Security | 15 days |
| Poor phishing detection | Improve email filtering | IT | 20 days |
| Delayed escalation | Update incident playbook | Security | 10 days |
| Employee awareness gap | Conduct phishing training | HR/Security | 30 days |
Actions should have:
- Owner
- Target date
- Priority
- Status
- Verification method
7. Update the Risk Assessment
An incident can provide evidence that an existing risk assessment was incomplete or underestimated.
For example:
Before incident:
Risk: Account compromise – Medium
After incident:
The organization discovers:
- Multiple users lack strong MFA
- Privileged accounts have excessive permissions
- Monitoring is insufficient
The organization may need to reassess the risk.
The incident should therefore feed back into the organization’s risk management process.
8. Update Policies and Procedures
If the incident identifies a weakness in a process, update the relevant documentation.
Examples:
- Incident Response Procedure
- Access Control Policy
- Password Policy
- MFA Standard
- Supplier Security Procedure
- Data Protection Procedure
- Backup Procedure
- Business Continuity Procedure
- Security Awareness Procedure
Documentation should reflect the actual improved process, not merely be changed to satisfy an audit.
9. Improve Technical Controls
Lessons learned may result in technical improvements.
Examples:
- Enable MFA
- Implement phishing-resistant authentication
- Reduce privileged access
- Improve endpoint detection
- Increase logging
- Improve SIEM rules
- Enable cloud security monitoring
- Improve backup protection
- Patch vulnerable systems
- Restrict administrative access
- Implement network segmentation
- Improve email security
10. Improve Employee Awareness and Training
Some incidents identify gaps in employee understanding.
Training may need to address:
- Phishing
- Social engineering
- Password security
- MFA
- Data handling
- Secure remote working
- Incident reporting
- Use of company systems
- Handling confidential information
However, training should not automatically be the only corrective action.
If a technical control can prevent or reduce the impact of an incident, the organization should consider strengthening that control as well.
11. Update Incident Response Playbooks
An incident may reveal that the existing response process was incomplete.
For example:
Original process:
Detect → Investigate → Recover
After the incident:
Detect → Triage → Contain → Preserve Evidence → Investigate → Eradicate → Recover → Communicate → Review
The updated process should reflect what the organization has learned.
12. Verify That Improvements Actually Worked
Corrective action should not end with:
“Action completed.”
The organization should verify effectiveness.
For example:
Problem: Excessive administrator privileges.
Action: Access rights reviewed.
Verification: Privileged access review performed and unnecessary permissions removed.
Effectiveness check: New quarterly access review confirms permissions remain appropriate.
This creates a continuous improvement cycle.
Startup Example – SaaS Company
Consider a SaaS startup with:
- AWS
- GitHub
- Google Workspace
- Jira
- Slack
- Customer production database
An employee’s Google Workspace account is compromised.
Initial response
The company:
- Disables the account
- Revokes active sessions
- Resets credentials
- Reviews authentication logs
- Checks access to company systems
- Investigates potential data exposure
- Restores normal operations
This addresses A.5.26 – Response to Information Security Incidents.
But the company should continue with A.5.27.
Post-incident review
The review discovers:
- MFA was enabled but not phishing-resistant
- Employee had excessive access
- Security alerts were not configured for unusual login locations
- Incident reporting instructions were unclear
- The response team spent too much time determining who should own the incident
Improvement actions
The company decides to:
- Implement stronger MFA
- Reduce employee privileges
- Configure additional identity alerts
- Update incident reporting instructions
- Update the incident response playbook
- Conduct security awareness training
- Review access rights for similar employees
- Update the risk assessment
The incident therefore becomes an opportunity to improve the overall security program.
Startup-Focused Quick Summary
For a startup, A.5.27 does not require creating a huge bureaucracy.
A practical process can be:
Incident → Review → Root Cause → Lessons → Corrective Actions → Risk Update → Verify
For every significant incident, ask:
- What happened?
- Why did it happen?
- What was the impact?
- What controls worked?
- What controls failed?
- What should change?
- Who owns the improvement?
- When should it be completed?
- How will we verify the improvement?
Simple Incident Learning Register
A startup can maintain a simple register like this:
| Incident ID | Incident | Root Cause | Lesson Learned | Action | Owner | Status |
|---|---|---|---|---|---|---|
| INC-001 | Phishing | Weak authentication | Stronger MFA required | Implement phishing-resistant MFA | IT | Open |
| INC-002 | Cloud exposure | Incorrect configuration | Cloud configuration review needed | Implement CSPM review | Security | Closed |
| INC-003 | Lost laptop | Device protection gap | Encryption must be verified | Enforce device encryption | IT | Closed |
This can be maintained in:
- Spreadsheet
- Jira
- ServiceNow
- GRC platform
- Ticketing system
- ISMS management system
The tool is less important than having a repeatable process and evidence of improvement.
Incident Learning Checklist
| Activity | Completed? |
|---|---|
| Incident formally closed | ☐ |
| Post-incident review completed | ☐ |
| Timeline documented | ☐ |
| Root cause identified | ☐ |
| Contributing factors identified | ☐ |
| Security controls evaluated | ☐ |
| Business impact evaluated | ☐ |
| Lessons learned documented | ☐ |
| Corrective actions identified | ☐ |
| Action owners assigned | ☐ |
| Target dates established | ☐ |
| Risk assessment reviewed | ☐ |
| Policies/procedures reviewed | ☐ |
| Technical controls reviewed | ☐ |
| Training requirements reviewed | ☐ |
| Incident playbook updated | ☐ |
| Corrective actions verified | ☐ |
| Lessons communicated to relevant personnel | ☐ |
Audit Evidence for A.5.27
An auditor may expect evidence that the organization actually learns from incidents.
Useful evidence includes:
Incident management
- Incident register
- Incident reports
- Incident closure records
- Incident timelines
Investigation
- Root cause analysis
- Investigation reports
- Technical analysis
- Impact assessment
Improvement
- Corrective action tracker
- Lessons learned register
- Risk register updates
- Updated policies
- Updated procedures
- Updated incident playbooks
Technical evidence
- Configuration changes
- Access reviews
- Security monitoring improvements
- Vulnerability remediation
- MFA implementation records
- Security tool configuration
People and awareness
- Training records
- Awareness communications
- Tabletop exercise results
Management
- Management review records
- Security committee meeting records
- ISMS improvement records
Audit Checklist – ISO 27001 A.5.27
An auditor may ask:
Incident Review
- Do you conduct post-incident reviews?
- Which incidents require formal review?
- Who performs the review?
- When is the review performed?
Root Cause
- How do you determine the root cause?
- Do you identify contributing factors?
- Do you distinguish the immediate cause from systemic weaknesses?
Lessons Learned
- How are lessons documented?
- How are lessons communicated?
- Do you identify recurring patterns?
Corrective Actions
- What actions resulted from previous incidents?
- Who owns those actions?
- Were they completed on time?
- How was effectiveness verified?
Risk Management
- Did the incident result in an update to the risk assessment?
- Were new risks identified?
- Were existing risk ratings or treatments reconsidered?
ISMS Improvement
- Did the organization modify controls or procedures?
- Were policies updated?
- Were incident-response procedures improved?
- Can you show evidence of continual improvement?
Common Mistakes in A.5.27
1. Closing the incident and doing nothing else
The technical problem is fixed and the incident is closed.
Problem: The underlying weakness remains.
2. Blaming an individual
For example:
“The employee clicked the phishing link, so the employee caused the incident.”
This may overlook:
- Weak authentication
- Poor email filtering
- Excessive access
- Lack of monitoring
- Insufficient awareness
- Weak incident reporting
A mature review looks at the system and contributing factors, not just individual behavior.
3. Fixing only the symptom
Example:
Password reset completed.
But the organization does not ask:
- Why was the account compromised?
- Was MFA sufficient?
- Were privileges excessive?
- Could the attack happen again?
4. Corrective actions have no owner
A report says:
“Improve access control.”
But nobody is responsible for doing it.
A better action is:
“Security Manager will complete privileged-access review for production systems by 15 October.”
5. No due dates
Without target dates, improvement actions can remain open indefinitely.
6. No effectiveness verification
An action can be marked “complete” even though the underlying risk remains.
7. Ignoring near misses
A security event that almost became an incident can provide valuable information.
Examples:
- Phishing email blocked at the last moment
- Vulnerability discovered before exploitation
- Misconfigured cloud storage detected before public exposure
Near misses can also contribute to organizational learning.
8. Failing to identify recurring incidents
If the organization experiences:
- Multiple phishing incidents
- Repeated access violations
- Repeated cloud misconfigurations
- Repeated endpoint infections
it should look for systemic causes rather than treating each incident independently.
Practical Startup Implementation Model
A startup can implement A.5.27 using six steps:
1. Review
Review significant incidents after stabilization.
↓
2. Understand
Determine what happened, why it happened, and what contributed to it.
↓
3. Learn
Identify weaknesses and lessons.
↓
4. Improve
Create corrective and preventive actions.
↓
5. Verify
Check whether the actions actually reduced the risk.
↓
6. Share
Communicate relevant lessons to employees, security teams, management, or suppliers.
Startup model
Review → Understand → Learn → Improve → Verify → Share
Policy vs. Process vs. Evidence
| Type | Example |
|---|---|
| Policy | Information Security Incident Management Policy |
| Process | Post-Incident Review Procedure |
| Template | Incident Review / Lessons Learned Template |
| Register | Lessons Learned Register |
| Evidence | Completed incident review |
| Improvement | Corrective action record |
| Verification | Effectiveness review |
| Risk Management | Updated risk assessment |
A startup does not need dozens of separate documents.
A well-designed Incident Management Procedure + Post-Incident Review Template + Corrective Action Register may be sufficient when supported by actual records.
Relationship with Other ISO 27001 Controls
A.5.27 works as part of the broader incident-management and continual-improvement cycle.
| Control | Relationship |
|---|---|
| A.5.24 | Establishes incident-management preparation |
| A.5.25 | Determines whether events should be treated as incidents |
| A.5.26 | Responds to incidents |
| A.5.27 | Learns from incidents and improves |
| A.5.28 | Supports evidence collection and preservation |
| A.5.35 | Independent review can evaluate security management |
| A.5.36 | Compliance with policies and standards can be reviewed |
| A.8.8 | Vulnerability management may be improved based on incidents |
| A.8.15 | Logging provides information for investigation and learning |
| A.8.16 | Monitoring helps identify detection and response weaknesses |
| A.8.32 | Change management helps control improvements resulting from incidents |
The overall cycle can be represented as:
A.5.24 Prepare
↓
A.5.25 Assess
↓
A.5.26 Respond
↓
A.5.28 Preserve Evidence
↓
A.5.27 Learn & Improve
↓
Update Risks, Controls & Procedures
Useful Documents for A.5.27
Organizations may maintain the following documents:
- Post-Incident Review Template
[Insert Draft Document Link] - Root Cause Analysis Template
[Insert Draft Document Link] - Lessons Learned Register
[Insert Draft Document Link] - Corrective Action Tracker
[Insert Draft Document Link] - Incident Trend Report
[Insert Draft Document Link] - ISMS Improvement Log
[Insert Draft Document Link] - Incident Response Playbook
[Insert Draft Document Link]
Questions an Auditor May Ask
An auditor may not simply ask:
“Do you have an incident policy?”
They may ask:
“Show me an incident from the last year and explain what you learned from it.”
They may then follow the evidence trail:
Incident → Investigation → Root Cause → Lesson → Corrective Action → Risk Update → Implementation → Verification
For example:
Incident: Compromised employee account
↓
Root Cause: Weak authentication and excessive privileges
↓
Lesson: Identity controls were insufficient
↓
Action: Stronger MFA + access review
↓
Risk Update: Account compromise risk reassessed
↓
Implementation: Controls implemented
↓
Verification: Follow-up access review and security testing
This demonstrates that the organization is actually using incidents to improve its ISMS.
Startup-Focused Final Takeaway
ISO 27001 Annex A 5.27 is about turning security incidents into organizational learning and measurable improvement.
A startup does not need an expensive GRC platform to implement this control.
A practical approach is:
Respond → Review → Understand → Learn → Improve → Verify
After every significant security incident, ask:
What happened?
Why did it happen?
What control failed or was missing?
What did we learn?
What are we changing?
Who owns the change?
How will we know the change worked?
The goal is not to create a perfect organization that never experiences a security incident.
The goal is to build an organization that learns from incidents, strengthens its controls, and becomes more resilient over time.
In one sentence:
A.5.27 ensures that security incidents become inputs for improving the organization’s security controls, risk management, processes, and ISMS—not just tickets that are closed.