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SIEM alerts on anomalous network traffic patterns requiring deeper investigation
C2 beaconing is suspected and needs confirmation through packet-level analysis
Data exfiltration volume or destination must be quantified from network evidence
Lateral movement between systems needs to be traced through network connections
An IDS/IPS alert requires packet-level validation to confirm or dismiss
Do not use for host-based forensic analysis (process execution, file system artifacts); use endpoint forensics tools instead.
Detection Gaps & Validation
Encrypted traffic is the #1 blind spot: without TLS inspection you cannot see C2 payloads. Pivot to metadata you do have — JA3/JA3S, SNI, certificate CN/issuer, packet timing, and request/response byte ratios. A self-signed cert plus fixed-interval beacons is enough to confirm without decryption.
Beacon jitter defeats naive interval checks: malware randomizes sleep (±30-50%) and long-haul beacons (1/hour or 1/day) fall outside a short capture. Use RITA/Zeek scoring over the full window, not a single PCAP slice, and account for jitter rather than requiring exact 60s spacing.
Capture coverage gaps: SPAN ports drop frames under load and a tap on one VLAN misses east-west lateral movement. Confirm capture completeness (capinfos drop counts, sequence gaps) before concluding "no exfil."
DNS/ICMP tunneling hides in low per-query volume: small TXT/A queries look benign individually — aggregate by parent domain and total bytes over time, and check entropy of subdomain labels.
Cross-corroborate: match the C2 IP/JA3 against threat intel, line up connection timestamps with host EDR process-start events (watch for timezone skew — normalize everything to UTC), and extract transferred files via Wireshark Export Objects / NetworkMiner to validate the exfil channel rather than inferring it from byte counts alone.
Prerequisites
Full packet capture (PCAP) infrastructure or on-demand capture capability (network tap, SPAN port)
Wireshark installed on the analysis workstation with appropriate display filters knowledge
# Large HTTP POST uploads
http.request.method == "POST" && tcp.len > 10000
# FTP data transfers
ftp-data && ip.src == 10.0.0.0/8
# DNS with large TXT responses (tunneling)
dns.resp.type == 16 && dns.resp.len > 200
Step 5: Extract and Correlate IOCs
Pull network-based indicators from traffic analysis:
External IP addresses contacted by compromised hosts
Domains resolved via DNS during the incident timeframe
URLs accessed via HTTP/HTTPS (if SSL inspection is in place)
TLS certificate details (subject, issuer, serial number, JA3/JA3S hashes)
User-Agent strings from HTTP requests
File transfers captured in PCAP (extract using Wireshark Export Objects)
Step 6: Document Network Forensic Findings
Compile analysis into a structured report with evidence references:
Reference specific PCAP files, frame numbers, and timestamps for each finding
Include packet captures of key evidence as screenshots or exported PDFs
Map network activity to the incident timeline
Correlate network findings with host-based evidence from endpoint forensics
Key Concepts
Term
Definition
PCAP (Packet Capture)
File format storing raw network packets captured from a network interface for offline analysis
Beaconing
Regular, periodic network connections from a compromised host to a C2 server, identifiable by consistent timing intervals
JA3/JA3S
TLS client and server fingerprinting method based on the ClientHello and ServerHello parameters; unique per application
NetFlow/IPFIX
Network traffic metadata (source, destination, ports, bytes, duration) collected by routers and switches without full packet capture
DNS Tunneling
Technique encoding data in DNS queries and responses to exfiltrate data or maintain C2 through DNS protocol
Network Tap
Hardware device that creates an exact copy of network traffic for monitoring without impacting network performance
Zeek Logs
Structured metadata logs generated by the Zeek network analysis framework covering connections, DNS, HTTP, SSL, and more
Tools & Systems
Wireshark: Open-source packet analyzer for deep inspection of network protocols at the packet level
Zeek (formerly Bro): Network analysis framework generating structured metadata logs from live or captured traffic
Arkime (formerly Moloch): Open-source full packet capture and search platform for large-scale network forensics
NetworkMiner: Network forensic analysis tool for extracting files, images, and credentials from PCAP files
RITA (Real Intelligence Threat Analytics): Open-source beacon detection and DNS tunneling analysis tool for Zeek logs
Common Scenarios
Scenario: Confirming C2 Beaconing and Quantifying Exfiltration
Context: EDR detects a suspicious process on a workstation but cannot determine the volume of data exfiltrated. Network team provides PCAP from the full packet capture appliance covering the incident timeframe.
Approach:
Filter PCAP to traffic from the compromised host IP to external destinations
Identify the C2 channel by analyzing connection timing patterns (beacon detection)
Extract TLS certificate and JA3 hash from the C2 connection for IOC generation
Calculate total bytes transferred to C2 infrastructure over the incident duration
Check for additional exfiltration channels (DNS tunneling, cloud storage uploads)
Extract any unencrypted files transferred using Wireshark Export Objects feature
Pitfalls:
Analyzing only HTTP traffic when C2 is operating over HTTPS without SSL inspection
Missing DNS tunneling because the data volume per query is small (but total over time is significant)
Not correlating network timestamps with endpoint timestamps (timezone mismatches)
Overlooking legitimate cloud services abused for exfiltration (OneDrive, Google Drive, Dropbox)
Output Format
NETWORK TRAFFIC ANALYSIS REPORT
=================================
Incident: INC-2025-1547
Analyst: [Name]
Capture Source: Arkime full packet capture
Analysis Period: 2025-11-15 14:00 UTC - 2025-11-15 18:00 UTC
Total PCAP Size: 4.7 GB
C2 COMMUNICATIONS
Source: 10.1.5.42 (WKSTN-042)
Destination: 185.220.101.42:443 (HTTPS)
Beacon Interval: 60 seconds ± 12% jitter
Sessions: 237 connections over 4 hours
JA3 Hash: a0e9f5d64349fb13191bc781f81f42e1
TLS Certificate: CN=update.evil[.]com (self-signed)
Total Data Sent: 147 MB (outbound)
Total Data Recv: 2.3 MB (inbound - commands)
LATERAL MOVEMENT
10.1.5.42 → 10.1.10.15 (SMB, TCP 445) - 14:35 UTC
10.1.5.42 → 10.1.10.20 (RDP, TCP 3389) - 14:42 UTC
10.1.5.42 → 10.1.1.5 (LDAP, TCP 389) - 15:10 UTC
EXFILTRATION SUMMARY
Protocol: HTTPS to C2 server
Volume: 147 MB outbound
Duration: 14:23 UTC - 18:00 UTC
Files Extracted: [list if recoverable from unencrypted channels]
DNS ANALYSIS
Suspicious Queries: 0 DNS tunneling indicators
DGA Detection: 0 algorithmically generated domains
EVIDENCE REFERENCES
PCAP File: INC-2025-1547_capture.pcap (SHA-256: ...)
Zeek Logs: /logs/zeek/2025-11-15/ (conn.log, ssl.log, dns.log)
