analyzing-command-and-control-communication

Analyzes malware C2 communication over HTTP, HTTPS, DNS, and custom protocols to reverse-engineer beacon patterns, command structures, data encoding, and infrastructure (primary servers, fallback domains, dead drops). Use after reverse engineering reveals network traffic needing protocol analysis or when building detection signatures for a framework like Cobalt Strike, Metasploit, or Sliver.

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リポジトリ: mukul975/Anthropic-Cybersecurity-Skills
ソースの最終更新活動: 2026年8月2日 16:32
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name	analyzing-command-and-control-communication
description	Analyzes malware C2 communication over HTTP, HTTPS, DNS, and custom protocols to reverse-engineer beacon patterns, command structures, data encoding, and infrastructure (primary servers, fallback domains, dead drops). Use after reverse engineering reveals network traffic needing protocol analysis or when building detection signatures for a framework like Cobalt Strike, Metasploit, or Sliver.
domain	cybersecurity
subdomain	malware-analysis
tags	["malware","C2","command-and-control","beacon","protocol-analysis"]
version	1.0.0
author	mahipal
license	Apache-2.0
nist_csf	["DE.AE-02","RS.AN-03","ID.RA-01","DE.CM-01"]
mitre_attack	["T1071.001","T1573","T1571","T1008","T1095"]

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

WebSocket:      Persistent bidirectional connection for real-time C2
                Indicators: WebSocket upgrade followed by binary frames

Cloud Services: Using legitimate APIs (Telegram, Discord, Slack, GitHub)
                Indicators: API calls to cloud services from unexpected processes

Email:          SMTP/IMAP for C2 commands and data exfiltration
                Indicators: Automated email operations from non-email processes

Step 2: Analyze Beacon Pattern

Characterize the periodic communication pattern:

from scapy.all  rdpcap, IP, TCP
 collections  defaultdict
 statistics
 json

packets = rdpcap()


connections = defaultdict()
 pkt  packets:
     IP  pkt  TCP  pkt  (pkt[TCP].flags & ):
        key = 
        connections[key].append((pkt.time))


 dst, times  (connections.items()):
     (times) < :
        

    intervals = [times[i+] - times[i]  i  ((times)-)]
    avg_interval = statistics.mean(intervals)
    stdev = statistics.stdev(intervals)  (intervals) >   
    jitter_pct = (stdev / avg_interval * )  avg_interval >   
    duration = times[-] - times[]

    beacon_data = {
        : dst,
        : (times),
        : (duration, ),
        : (avg_interval, ),
        : (stdev, ),
        : (jitter_pct, ),
        :  < avg_interval <   jitter_pct < ,
    }

     beacon_data[]:
        ()
        ()
        ()

# HTTP-based C2 protocol analysis
import dpkt
import base64

with open("c2_traffic.pcap", "rb") as f:
    pcap = dpkt.pcap.Reader(f)

for ts, buf in pcap:
    eth = dpkt.ethernet.Ethernet(buf)
    if not isinstance(eth.data, dpkt.ip.IP):
        continue
    ip = eth.data
    if not isinstance(ip.data, dpkt.tcp.TCP):
        continue
    tcp = ip.data

    if tcp.dport == 80 or tcp.dport == 443:
        if len(tcp.data) > 0:
            try:
                http = dpkt.http.Request(tcp.data)
                print(f"\n--- C2 REQUEST ---")
                print(f"Method: {http.method}")
                print(f"URI: {http.uri}")
                print(f"Headers: {dict(http.headers)}")
                if http.body:
                    print(f"Body ({len(http.body)} bytes):")
                    # Try Base64 decode
                    try:
                        decoded = base64.b64decode(http.body)
                        print(f"  Decoded: {decoded[:200]}")
                    except:
                        print(f"  Raw: {http.body[:200]}")
            except:
                pass

Known C2 Framework Signatures:
━━━━━━━━━━━━━━━━━━━━━━━━━━━━
Cobalt Strike:
  - Default URIs: /pixel, /submit.php, /___utm.gif, /ca, /dpixel
  - Malleable C2 profiles customize all traffic characteristics
  - JA3: varies by profile, catalog at ja3er.com
  - Watermark in beacon config (unique per license)
  - Config extraction: use CobaltStrikeParser or 1768.py

Metasploit/Meterpreter:
  - Default staging URI patterns: random 4-char checksum
  - Reverse HTTP(S) handler patterns
  - Meterpreter TLV (Type-Length-Value) protocol structure

Sliver:
  - mTLS, HTTP, DNS, WireGuard transport options
  - Protobuf-encoded messages
  - Unique implant ID in communication

Covenant:
  - .NET-based C2 framework
  - HTTP with customizable profiles
  - Task-based command execution

PoshC2:
  - PowerShell/C# based
  - HTTP with encrypted payloads
  - Cookie-based session management

# Extract Cobalt Strike beacon configuration from PCAP or sample
python3 << 'PYEOF'
# Using CobaltStrikeParser (pip install cobalt-strike-parser)
from cobalt_strike_parser import BeaconConfig

try:
    config = BeaconConfig.from_file("suspect.exe")
    print("Cobalt Strike Beacon Configuration:")
    for key, value in config.items():
        print(f"  {key}: {value}")
except Exception as e:
    print(f"Not a Cobalt Strike beacon or parse error: {e}")
PYEOF

# Infrastructure mapping
import requests
import json

c2_indicators = {
    "primary_c2": "185.220.101.42",
    "domains": ["update.malicious.com", "backup.evil.net"],
    "ports": [443, 8443],
    "failover_dns": ["ns1.malicious-dns.com"],
}

# Enrich with Shodan
def shodan_lookup(ip, api_key):
    resp = requests.get(f"https://api.shodan.io/shodan/host/{ip}?key={api_key}")
    if resp.status_code == 200:
        data = resp.json()
        return {
            "ip": ip,
            "ports": data.get("ports", []),
            "os": data.get("os"),
            "org": data.get("org"),
            "asn": data.get("asn"),
            "country": data.get("country_code"),
            "hostnames": data.get("hostnames", []),
            "last_update": data.get("last_update"),
        }
    return None

# Enrich with passive DNS
def pdns_lookup(domain):
    # Using VirusTotal passive DNS
    resp = requests.get(
        f"https://www.virustotal.com/api/v3/domains/{domain}/resolutions",
        headers={"x-apikey": VT_API_KEY}
    )
    if resp.status_code == 200:
        data = resp.json()
        resolutions = []
        for r in data.get("data", []):
            resolutions.append({
                "ip": r["attributes"]["ip_address"],
                "date": r["attributes"]["date"],
            })
        return resolutions
    return []

# Suricata rules for the analyzed C2
cat << 'EOF' > c2_detection.rules
# HTTP beacon pattern
alert http $HOME_NET any -> $EXTERNAL_NET any (
    msg:"MALWARE MalwareX C2 HTTP Beacon";
    flow:established,to_server;
    http.method; content:"POST";
    http.uri; content:"/gate.php"; startswith;
    http.header; content:"User-Agent: Mozilla/5.0 (compatible; MSIE 10.0)";
    threshold:type threshold, track by_src, count 5, seconds 600;
    sid:9000010; rev:1;
)

# JA3 fingerprint match
alert tls $HOME_NET any -> $EXTERNAL_NET any (
    msg:"MALWARE MalwareX TLS JA3 Fingerprint";
    ja3.hash; content:"a0e9f5d64349fb13191bc781f81f42e1";
    sid:9000011; rev:1;
)

# DNS beacon detection (high-entropy subdomain)
alert dns $HOME_NET any -> any any (
    msg:"MALWARE Suspected DNS C2 Tunneling";
    dns.query; pcre:"/^[a-z0-9]{20,}\./";
    threshold:type threshold, track by_src, count 10, seconds 60;
    sid:9000012; rev:1;
)

# Certificate-based detection
alert tls $HOME_NET any -> $EXTERNAL_NET any (
    msg:"MALWARE MalwareX Self-Signed C2 Certificate";
    tls.cert_subject; content:"CN=update.malicious.com";
    sid:9000013; rev:1;
)
EOF

Term	Definition
Beaconing	Periodic check-in communication from malware to C2 server at regular intervals, often with jitter to avoid pattern detection
Jitter	Randomization applied to beacon interval (e.g., 60s +/- 15%) to make the timing pattern less predictable and harder to detect
Malleable C2	Cobalt Strike feature allowing operators to customize all aspects of C2 traffic (URIs, headers, encoding) to mimic legitimate services
Dead Drop	Intermediate location (paste site, cloud storage, social media) where C2 commands are posted for the malware to retrieve
Domain Fronting	Using a trusted CDN domain in the TLS SNI while routing to a different backend, making C2 traffic appear to go to a legitimate service
Fast Flux	Rapidly changing DNS records for C2 domains to distribute across many IPs and resist takedown efforts
C2 Framework	Software toolkit providing C2 server, implant generator, and operator interface (Cobalt Strike, Metasploit, Sliver, Covenant)

C2 COMMUNICATION ANALYSIS REPORT
===================================
Sample:           malware.exe (SHA-256: e3b0c44...)
C2 Framework:     Cobalt Strike 4.9

BEACON CONFIGURATION
C2 Server:        hxxps://185.220.101[.]42/updates
Beacon Type:      HTTPS (reverse)
Sleep:            60 seconds
Jitter:           15%
User-Agent:       Mozilla/5.0 (Windows NT 10.0; Win64; x64)
URI (GET):        /dpixel
URI (POST):       /submit.php
Watermark:        1234567890

PROTOCOL ANALYSIS
Transport:        HTTPS (TLS 1.2)
JA3 Hash:         a0e9f5d64349fb13191bc781f81f42e1
Certificate:      CN=Microsoft Update (self-signed)
Encoding:         Base64 with XOR key 0x69
Command Format:   [4B length][4B command_id][payload]

COMMAND SET
0x01 - Sleep          Change beacon interval
0x02 - Shell          Execute cmd.exe command
0x03 - Download       Transfer file from C2
0x04 - Upload         Exfiltrate file to C2
0x05 - Inject         Process injection
0x06 - Keylog         Start keylogger
0x07 - Screenshot     Capture screen

INFRASTRUCTURE
Primary:          185.220.101[.]42 (AS12345, Hosting Co, NL)
Failover:         91.215.85[.]17 (AS67890, VPS Provider, RU)
DNS:              update.malicious[.]com -> 185.220.101[.]42
Registrar:        NameCheap
Registration:     2025-09-01

DETECTION SIGNATURES
SID 9000010:      HTTP beacon pattern
SID 9000011:      JA3 TLS fingerprint
SID 9000013:      C2 certificate match