Exfiltration Assessment

Description: Investigating data exfiltration forensically on workstations and server systems involves identifying and analysing how sensitive data was transferred from the network. This process is critical in understanding the scope of a security breach. Exfiltration can occur in various ways, including unauthorised email transmissions, external storage devices, cloud storage uploads, and covert channels.

1. Understanding Common Exfiltration Techniques

• Email Transmission: Unauthorised sending of sensitive data via email.

• Removable Media: Copying data to USB drives or other removable media.

• Network Transfer: Utilising FTP, HTTP, or other protocols to transfer data to external servers.

• Cloud Storage: Uploading data to cloud storage services.

• Encrypted Channels: Using VPNs, SSH tunnels, or other encrypted methods to hide data transmission.

2. Data Collection and Preservation

• Forensic Imaging: Create exact images of the hard drives of affected systems using tools like FTK Imager or dd.

• Memory Capture: Use tools like Magnet RAM Capture or WinPmem to capture volatile memory.

• Log Collection: Gather network logs, firewall logs, system logs, and application logs.

3. Email Analysis

• Email Server Logs: Review logs for signs of large email transmissions or emails sent to unusual external addresses.

• Email Client Analysis: Examine the email clients on affected systems for sent items, drafts, or deleted emails.

4. Removable Media Analysis

• USB Device History: Windows stores a history of connected USB devices in the registry. Examine this for evidence of any unknown devices.

• File System Analysis: Check for recently accessed files or file copies that coincide with the connection times of external media.

5. Network Traffic Analysis

• Network Monitoring Tools: Use tools like Wireshark or Tcpdump to analyse captured network traffic for data transfers to unusual external IP addresses.

• Firewall and Proxy Logs: Review logs for large data transfers or connections to known file-sharing or cloud storage sites.

6. Cloud Storage and Web Uploads

• Browser History and Cookies: Examine web browser history and cookies to access cloud storage websites.

• Web Proxy Logs: Analyse web proxy logs for uploads to cloud services.

7. Analysing Encrypted Traffic

• Decrypting Traffic: Where possible and legal, decrypt encrypted network traffic to inspect the contents.

• TLS/SSL Certificate Analysis: Review certificates for any unrecognised or self-signed certificates that may have been used in exfiltration.

8. File Access and Movement Analysis

• File Access Logs: Review logs for accessed files containing sensitive information.

• Recent Documents and File Timestamps: Examine recent documents and file timestamps for evidence of copying or accessing large volumes of data.

9. Use of Specialised Forensic Tools

• Forensic Suites: Tools like EnCase, Autopsy, or AXIOM Cyber for comprehensive analysis.

• Network Analysis Tools: Wireshark, Tcpdump, NetWitness for network traffic analysis.

10. Documentation and Reporting

• Detailed Documentation: Keep a detailed record of all findings, tools used, and investigative processes.

• Forensic Report: Prepare a comprehensive report detailing the exfiltration methods identified, data compromised, and impact assessment.

11. Post-Investigation Actions

• Mitigation and Remediation: Implement necessary security measures to prevent future incidents.

• Recovery and Notifications: Follow organisational and legal protocols for data breach response, including notifying affected parties if necessary.

12. Tools and Techniques

• Digital Forensics:

  • Specialised tools for evidence collection and analysis:

    • OpenText EnCase Forensics (commercial tool)

    • FTK (Forensic Toolkit)

    • Volatility (memory forensics)

    • Autopsy (open-source)

    • Cyber Triage (commercial tool)

    • Binalyze AIR (commercial tool)

    • Belkasoft (commercial tool)

    • Oxygen Forensics (commercial tool)

    • X-ways Forensics (commercial tool)

    • The Sleuth Kit (open-source tool)

    • Eric Zimmerman Tools (open-source tool)

  • Techniques include timeline analysis, file recovery, and reverse engineering.

• Incident Response:

  • Tools for monitoring, containment, and eradication:

    • SIEM (Splunk, QRadar, Microsoft Sentinel, Sumo Logic, Graylog, Elastic Security, LogRhythm, Datadog, Exabeam)

    • EDR (CrowdStrike, SentinelOne, Defender for Endpoint, Cortex XDR, FortiEDR)

    • Firewalls and IDS/IPS systems

  • Techniques include log analysis, threat containment, and system restoration.

13. Key Considerations

• Legal Compliance: Ensure the investigation complies with legal and regulatory requirements, especially when dealing with encrypted traffic and privacy-sensitive data.

• Data Confidentiality: Maintain strict confidentiality and integrity of data throughout the investigation process.

• Chain of Custody: Maintain a clear chain of custody for all evidence collected.

Forensic investigations of data exfiltration require careful analysis of various data sources and the application of appropriate forensic techniques. Tailoring the investigation to the specifics of the incident and the nature of the data involved is crucial.