Exercise 35: Network Forensics – Investigating a Breach

Objective

Perform forensic analysis on network traffic to investigate a potential security breach by identifying suspicious activities and proposing preventive measures.

Scenario

You are part of the incident response team investigating a suspected data breach within your organization. A PCAP file containing captured network traffic has been provided. Your task is to analyze the file, uncover any malicious activities such as data exfiltration or unauthorized access, and document the evidence. Additionally, you must propose security measures to prevent similar incidents.

⚠️ Important: This exercise should be conducted in a legal and controlled environment. Always handle network data with confidentiality and integrity.

Lab Instructions

Step 1: Set Up the Analysis Environment

• Install the required tools on your analysis machine:
  • Wireshark: For in-depth packet analysis.
  • tcpdump: For quick command-line packet review.
  • NetworkMiner (optional): For passive network analysis.

a. Install Wireshark

sudo apt update
sudo apt install wireshark -y

b. Install tcpdump

sudo apt install tcpdump -y

Step 2: Analyze the PCAP File

a. Load the PCAP File into Wireshark

wireshark breach_capture.pcap

b. Apply Filters to Identify Suspicious Traffic

• Filter for external connections:

ip.dst != 192.168.1.0/24 && ip.src == 192.168.1.0/24

• Filter for file transfers (HTTP/FTP):

ftp || http || tcp.port == 21 || tcp.port == 80

• Filter for DNS tunneling:

dns && frame.len > 200

c. Identify Unauthorized Access

• Look for unusual login attempts:

ftp.request.command == "USER" || ftp.request.command == "PASS"

• Check for remote connections:

tcp.port == 22 || tcp.port == 3389

d. Analyze for Data Exfiltration

• Identify large outbound data transfers:

ip.src == 192.168.1.0/24 && tcp.len > 1000

• Look for base64-encoded payloads in HTTP traffic:

http.request.uri contains "="

Step 3: Document Findings

a. Evidence Table

b. Suspicious Indicators

• Multiple failed FTP login attempts.
• Large file transfers to external IPs.
• DNS queries with unusually large payloads.

Step 4: Propose Preventive Measures

1. Implement Intrusion Detection Systems (IDS): Deploy IDS tools like Snort or Zeek to monitor for unusual traffic.
2. Enforce Access Controls: Apply least privilege principles to limit user access to sensitive systems.
3. Restrict Outbound Traffic: Configure firewall rules to block unnecessary outbound connections.
4. Enable Multi-Factor Authentication (MFA): Add an extra layer of security for remote access services.
5. Regular Patch Management: Keep all systems and applications updated to fix vulnerabilities.
6. Log Monitoring and Analysis: Continuously monitor logs for signs of malicious activity.
7. DNS Security: Implement DNS filtering and disable external DNS resolution where not required.

Step 5: Verify Security Enhancements

• Simulate similar attack scenarios to test the effectiveness of the applied security measures.
• Monitor system logs and network traffic for any anomalies.

Solution & Explanation

What is Network Forensics?

• Network forensics involves capturing, recording, and analyzing network traffic to detect and investigate security incidents.

Indicators of a Data Breach

• Unauthorized Access: Repeated login attempts, access from unusual IP addresses.
• Data Exfiltration: Large outbound data transfers, encrypted payloads.
• Anomalous DNS Traffic: DNS tunneling or suspicious domain queries.

Preventive Measures

• Proactive Monitoring: Use IDS/IPS systems to detect threats early.
• Access Restrictions: Minimize user permissions and network exposure.
• Traffic Filtering: Implement strict firewall and egress filtering rules.

Testing & Verification

• Simulate Data Exfiltration: Attempt file transfers and verify detection.
• Monitor IDS/Firewall Logs: Check for alerts related to unauthorized access or data transfers.
• Run Vulnerability Scans: Identify misconfigurations or outdated systems.

Security Best Practices

1. Use Encrypted Protocols: Replace FTP with SFTP or FTPS.
2. Implement Security Policies: Define and enforce network access policies.
3. Regular Security Training: Educate employees on phishing and social engineering.
4. Data Loss Prevention (DLP): Deploy DLP solutions to detect and block sensitive data exfiltration.

Additional Script (Optional)

Automate suspicious traffic detection with tcpdump:

#!/bin/bash
# Monitor for large outbound transfers
sudo tcpdump -i eth0 'tcp and (dst portrange 20-21 or dst port 80)' and 'greater 1000' -w suspicious_traffic.pcap

Run the script:

chmod +x monitor_traffic.sh
sudo ./monitor_traffic.sh

Conclusion

In this exercise, you performed a forensic analysis of network traffic to investigate a simulated data breach. You identified suspicious activity, documented evidence, and proposed preventive measures to mitigate future incidents. Mastery of network forensics is essential for detecting, analyzing, and responding to security breaches.