Incident Response Playbook for Malicious Network Behaviour (Updated 2025)

This Malicious Network Behaviour Incident Response Playbook provides a systematic approach to detecting, containing, remediating, and recovering from suspicious network activity. It has been updated to incorporate modern techniques such as advanced traffic monitoring, endpoint detection, and integration with threat intelligence platforms.

1. Preparation

Objective: Establish tools, procedures, and contacts to facilitate efficient incident handling and minimise response times.

Key Steps:

1. Deploy Security Tools:

   • Ensure Intrusion Detection Systems (IDS), Intrusion Prevention Systems (IPS), Network Intrusion Detection Systems (NIDS), and Endpoint Detection and Response (EDR) tools are deployed and up to date.

   • Implement network monitoring tools such as NetFlow or Suricata to track traffic patterns and detect anomalies.

2. Document and Maintain Network Information:

   • Keep an updated inventory of network devices, access points, and configurations.

   • Ensure that network topology diagrams are accessible and version-controlled.

3. Establish Baseline Traffic Patterns:

   • Define normal traffic flow and critical business services to quickly identify deviations.

   • Monitor and log network performance indicators, including bandwidth utilisation, protocol usage, and common communication endpoints.

4. Prepare Response Procedures:

   • Define roles for SOC analysts, network administrators, and response teams.

   • Maintain secure communication channels for incident coordination.

5. Configure Logging and Retention:

   • Ensure logs are collected from key systems (e.g., firewalls, routers, proxies) and retained for a minimum period (e.g., six months or more).

   • Enable centralised log storage with secure access control.

2. Identification

Objective: Detect and confirm malicious activity on the network, assess its scope, and notify relevant stakeholders.

Steps:

1. Monitor Detection Sources:

   • Analyse alerts from:

     • IDS/IPS, NIDS, and EDR logs.

     • Network monitoring tools.

     • Firewall and proxy logs.

   • Look for notifications from users, helpdesk reports, or external sources such as threat intelligence providers.

2. Capture Network Traffic:

   • Use tools such as tcpdump, Wireshark, or TShark to capture and analyse network traffic.

   • Enable port mirroring or use hubs to capture data from affected network segments.

3. Analyse Malicious Traffic:

   • Review network traffic for key indicators:

     • Source and destination IP addresses.

     • Ports, protocols, and TTL (time-to-live) values.

     • Packet payloads and IDs.

     • Exploits, suspicious user-agent strings, and remote login attempts.

   • Correlate findings with business operations to determine criticality.

4. Identify Impacted Systems:

   • Map malicious traffic to targeted devices or services.

   • Begin preliminary forensic investigations to determine whether system compromises have occurred.

3. Containment

Objective: Limit the impact of malicious activity by isolating compromised systems and blocking further attacks.

Steps:

1. Isolate Compromised Areas:

   • Disconnect affected network segments or endpoints to prevent the spread of malicious activity.

   • Apply quarantine rules via EDR tools or network access control (NAC) systems.

2. Implement Temporary Mitigation:

   • Block malicious IP addresses, domains, and traffic patterns using firewall and IPS rules.

   • Use multi-factor authentication (MFA) and geo-restrictions to secure critical systems.

3. Terminate Malicious Connections:

   • Identify and kill suspicious processes or network connections on compromised machines.

   • Enable verbose logging to capture detailed activity for forensic analysis.

4. Communication with Business Teams:

   • Inform business stakeholders about temporary network changes and limitations.

   • Ensure ongoing communication with executive management and incident coordinators.

4. Remediation

Objective: Stop the attack, remove all malicious artefacts, and close any vulnerabilities used by the attacker.

Steps:

1. Block Communication Channels:

   • Identify all communication channels exploited by the attacker and block them at all network boundaries (firewalls, routers, IDS/IPS).

2. Remove Malicious Components:

   • Use EDR tools to scan for and eliminate malware, backdoors, or modified configurations.

   • Remove any unauthorised accounts or scheduled tasks created by attackers.

3. Conduct Insider or External Investigations:

   • If an insider threat is suspected, coordinate with HR and legal teams.

   • If an external attack is confirmed, consider notifying law enforcement or CERT teams.

4. Test and Validate:

   • Test the remediation measures in a controlled environment.

   • Ensure no essential services are disrupted before applying the changes to production.

5. Recovery

Objective: Restore systems and network services to normal operation, ensuring that no residual threats remain.

Steps:

1. Re-enable Network Connectivity:

   • Gradually reintroduce previously disconnected network segments and endpoints.

   • Monitor network traffic closely for signs of persistent or recurring malicious activity.

2. System Verification:

   • Verify that all affected systems and services are operational.

   • Conduct integrity checks on key files, configurations, and applications.

3. Credential and Access Management:

   • Enforce a global password reset for compromised accounts.

   • Strengthen access controls and implement MFA across critical services.

6. Lessons Learned

Objective: Review and document the incident to improve future incident handling and enhance network defences.

Steps:

1. Document Incident Details:

   • Create a report that includes:

     • Timeline of events.

     • Root cause analysis.

     • Actions taken during containment and remediation.

     • Indicators of compromise (IOCs) and attack methods.

2. Evaluate Performance:

   • Conduct a post-incident review with all stakeholders.

   • Identify gaps in detection, response, and communication processes.

3. Update Playbooks:

   • Incorporate lessons learned into response procedures and detection rules.

   • Implement additional training and awareness programs for SOC analysts and IT teams.

4. Enhance Defences:

   • Improve network segmentation, access control, and monitoring capabilities.

   • Integrate new threat intelligence sources to strengthen proactive defence measures.

Conclusion

This Malicious Network Behaviour Playbook provides a comprehensive approach to detecting, mitigating, and remediating suspicious network activity. Regular testing and updates to the playbook will ensure continued readiness to handle evolving network threats.

For additional resources, including network analysis tools, communication templates, or reporting guidelines, please contact our cybersecurity team.