Analyzing Command-and-Control Communication

When to Use

• Reverse engineering a malware sample has revealed network communication that needs protocol analysis
• Building network-level detection signatures for a specific C2 framework (Cobalt Strike, Metasploit, Sliver)
• Mapping C2 infrastructure including primary servers, fallback domains, and dead drops
• Analyzing encrypted or encoded C2 traffic to understand the command set and data format
• Attributing malware to a threat actor based on C2 infrastructure patterns and tooling

Do not use for general network anomaly detection; this is specifically for understanding known or suspected C2 protocols from malware analysis.

Prerequisites

• PCAP capture of malware network traffic (from sandbox, network tap, or full packet capture)
• Wireshark/tshark for packet-level analysis
• Reverse engineering tools (Ghidra, dnSpy) for understanding C2 code in the malware binary
• Python 3.8+ with scapy, dpkt, and requests for protocol analysis and replay
• Threat intelligence databases for C2 infrastructure correlation (VirusTotal, Shodan, Censys)
• JA3/JA3S fingerprint databases for TLS-based C2 identification

Workflow

Step 1: Identify the C2 Channel

Determine the protocol and transport used for C2 communication:

C2 Communication Channels:
━━━━━━━━━━━━━━━━━━━━━━━━━
HTTP/HTTPS:     Most common; uses standard web traffic to blend in
                Indicators: Regular POST/GET requests, specific URI patterns, custom headers

DNS:            Tunneling data through DNS queries and responses
                Indicators: High-volume TXT queries, long subdomain names, high entropy

Custom TCP/UDP: Proprietary binary protocol on non-standard port
                Indicators: Non-HTTP traffic on high ports, unknown protocol

ICMP:           Data encoded in ICMP echo/reply payloads
                Indicators: ICMP packets with large or non-standard payloads