Digital forensics involves the preservation, identification, extraction, and documentation of computer evidence. When critical infrastructure is compromised, prompt and effective digital forensic investigations are paramount to understand the breach, mitigate the damage, and prevent future incidents.

Preliminary Steps

Before beginning an investigation, certain preliminary steps should be taken:

• Incident Reporting: Ensure the incident is reported to the relevant authorities and stakeholders.
• Incident Response Plan Activation: Activate the organization’s incident response plan and assemble the incident response team.

Setting Up for the Investigation

• Securing the Environment: Ensure the physical and digital environment is secure to prevent additional data loss or further compromise.
• Legal Considerations: Understand the legal implications and ensure all processes adhere to relevant laws and regulations.

Evidence Preservation

Preserve evidence to maintain its integrity:

• Chain of Custody Documentation: Document every step taken, including who handled evidence and when.
• Data Acquisition: Securely copy digital evidence using write-blocking tools to prevent data tampering.
• Hashing: Create cryptographic hashes of all evidence to verify it remains unaltered throughout the investigation.

Identification

Identify relevant systems and data:

• Systems Inventory: Compile a list of all affected systems, including hardware and software configurations.
• Access Logs: Gather access logs to identify potential entry points and trace suspicious activities.
• Network Traffic: Analyze network traffic to and from the compromised systems for anomalies.

Extraction

Extract data meticulously:

• Create Forensic Images: Make bit-by-bit copies of storage media for analysis.
• Capture Volatile Data: Record data stored in memory, such as running processes and network connections, as it could be lost upon power down.
• Data Carving: Use specialized tools to extract data remnants not readily accessible or that may have been deleted.

Examination

Analyze the evidence collected:

• Timeline Analysis: Establish a timeline of events to understand the sequence of the breach.
• Log Analysis: Examine system and event logs for signs of unauthorized access or changes.
• Malware Analysis: Search for and analyze any malware artifacts that could reveal the attack vector or the nature of the breach.

Analysis

Dive deeper into evidence:

• Correlation: Correlate data from multiple sources to build a comprehensive picture of the incident.
• Anomaly Detection: Use anomaly detection techniques to highlight unusual activity patterns.
• Intrusion Detection: Review intrusion detection system (IDS) alerts for indications of compromise.

Reporting

Communicate findings:

• Findings Summary: Provide a detailed summary of the investigation’s findings, including the cause and extent of the breach.
• Impact Assessment: Assess the impact of the incident on the organization’s operations.
• Mitigation Steps: Outline steps taken to mitigate the breach and suggestions for future prevention.
• Lessons Learned: Document any lessons learned and recommended improvements to the organization’s security posture.

Follow-Up Actions

• Remediation: Execute a plan to address vulnerabilities and secure systems.
• Monitoring: Implement heightened monitoring to detect any signs of persistent threats or follow-up attacks.
• Legal Action: Use the digital forensic report to take legal action if necessary.
• Stakeholder Communication: Keep stakeholders informed throughout the remediation and recovery process.

It’s worth noting that digital forensic investigations for compromised critical infrastructure require collaboration with various stakeholders and, often, external experts or law enforcement agencies. Each investigation is unique, and the steps taken may vary depending on the incident’s specifics. The ultimate goal of a digital forensic investigation in this context is to understand the incident thoroughly, improve cyber resilience, and assist in bringing perpetrators to justice.