analyzing-network-traffic-of-malware

What this skill does

# Analyzing Network Traffic of Malware

## When to Use

- Sandbox execution has captured a PCAP file and the network behavior needs detailed analysis
- Identifying the C2 protocol structure for writing network detection signatures
- Determining what data the malware exfiltrates and to which external infrastructure
- Analyzing DNS tunneling, domain generation algorithms (DGA), or fast-flux behavior
- Creating Suricata/Snort signatures based on observed malware network patterns

**Do not use** for host-based analysis of malware behavior; use Cuckoo sandbox reports or Volatility memory analysis for process-level activity.

## Prerequisites

- Wireshark 4.x installed for interactive PCAP analysis
- tshark (Wireshark CLI) for scripted packet extraction
- Zeek installed for automated metadata generation from PCAPs
- Suricata with ET Open/ET Pro rulesets for signature matching
- NetworkMiner for file extraction and credential detection from PCAPs
- Python 3.8+ with `scapy` and `dpkt` for programmatic packet analysis

## Workflow

### Step 1: Initial PCAP Overview

Get a high-level understanding of the network traffic:

```bash
# Capture statistics
capinfos malware.pcap

# Protocol hierarchy
tshark -r malware.pcap -q -z io,phs

# Endpoint statistics (top talkers)
tshark -r malware.pcap -q -z endpoints,ip

# Conversation statistics
tshark -r malware.pcap -q -z conv,tcp

# DNS query summary
tshark -r malware.pcap -q -z dns,tree
```

### Step 2: Analyze DNS Activity

Examine DNS queries for DGA, tunneling, or C2 domain resolution:

```bash
# Extract all DNS queries
tshark -r malware.pcap -T fields -e frame.time -e dns.qry.name -e dns.a \
  -Y "dns.flags.response == 1" | sort

# Detect DGA patterns (high entropy domain names)
python3 << 'PYEOF'
import math
from collections import Counter

def entropy(s):
    p = [n/len(s) for n in Counter(s).values()]
    return -sum(pi * math.log2(pi) for pi in p if pi > 0)

# Parse DNS queries from tshark output
import subprocess
result = subprocess.run(
    ["tshark", "-r", "malware.pcap", "-T", "fields", "-e", "dns.qry.name",
     "-Y", "dns.flags.response == 0"],
    capture_output=True, text=True
)

domains = set(result.stdout.strip().split('\n'))
print("Suspicious DNS queries (high entropy):")
for domain in domains:
    if domain:
        subdomain = domain.split('.')[0]
        ent = entropy(subdomain)
        if ent > 3.5 and len(subdomain) > 10:
            print(f"  {domain} (entropy: {ent:.2f})")
PYEOF

# Detect DNS tunneling (large TXT responses)
tshark -r malware.pcap -T fields -e dns.qry.name -e dns.txt \
  -Y "dns.resp.type == 16 and dns.resp.len > 100"
```

### Step 3: Analyze HTTP/HTTPS C2 Communication

Examine web-based command-and-control traffic:

```bash
# Extract HTTP requests
tshark -r malware.pcap -T fields \
  -e frame.time -e ip.src -e ip.dst -e http.host \
  -e http.request.method -e http.request.uri -e http.user_agent \
  -Y "http.request"

# Extract HTTP response bodies (potential payload downloads)
tshark -r malware.pcap -T fields \
  -e http.host -e http.request.uri -e http.content_type -e tcp.len \
  -Y "http.response and tcp.len > 1000"

# Extract POST data (potential exfiltration)
tshark -r malware.pcap -T fields \
  -e http.host -e http.request.uri -e http.file_data \
  -Y "http.request.method == POST"

# TLS analysis (SNI, JA3 fingerprints)
tshark -r malware.pcap -T fields \
  -e tls.handshake.extensions_server_name \
  -e tls.handshake.ja3 \
  -Y "tls.handshake.type == 1"

# Extract TLS certificate details
tshark -r malware.pcap -T fields \
  -e x509ce.dNSName -e x509af.serialNumber \
  -e x509sat.utf8String \
  -Y "tls.handshake.type == 11"

# Export HTTP objects (downloaded files)
tshark -r malware.pcap --export-objects http,exported_files/
```

### Step 4: Detect Beaconing Patterns

Identify regular periodic communication indicating C2 beaconing:

```python
# Beacon detection from PCAP
from scapy.all import rdpcap, IP, TCP
from collections import defaultdict
import statistics

packets = rdpcap("malware.pcap")

# Group connections by destination IP:port
connections = defaultdict(list)
for pkt in packets:
    if IP in pkt and TCP in pkt:
        if pkt[TCP].flags & 0x02:  # SYN flag
            dst = f"{pkt[IP].dst}:{pkt[TCP].dport}"
            connections[dst].append(float(pkt.time))

# Analyze timing intervals for beaconing
print("Beacon Analysis:")
for dst, times in connections.items():
    if len(times) >= 5:
        intervals = [times[i+1] - times[i] for i in range(len(times)-1)]
        avg = statistics.mean(intervals)
        stdev = statistics.stdev(intervals) if len(intervals) > 1 else 0
        jitter = (stdev / avg * 100) if avg > 0 else 0

        if 10 < avg < 3600 and jitter < 30:  # Regular interval with < 30% jitter
            print(f"  [!] {dst}: {len(times)} connections")
            print(f"      Interval: {avg:.1f}s ± {stdev:.1f}s (jitter: {jitter:.1f}%)")
            print(f"      Pattern: LIKELY BEACONING")
```

### Step 5: Generate Network Detection Signatures

Create Suricata/Snort rules from observed traffic patterns:

```bash
# Run Suricata against the PCAP for existing signature matches
suricata -r malware.pcap -l suricata_output/ -c /etc/suricata/suricata.yaml

# Review alerts
cat suricata_output/fast.log

# Create custom Suricata rule from observed patterns
cat << 'EOF' > custom_malware.rules
# C2 beacon detection based on observed URI pattern
alert http $HOME_NET any -> $EXTERNAL_NET any (
    msg:"MALWARE MalwareX C2 Beacon";
    flow:established,to_server;
    http.method; content:"POST";
    http.uri; content:"/gate.php?id=";
    http.user_agent; content:"Mozilla/5.0 (compatible; MSIE 10.0)";
    sid:9000001; rev:1;
)

# DNS query for known C2 domain
alert dns $HOME_NET any -> any any (
    msg:"MALWARE MalwareX C2 DNS Query";
    dns.query; content:"update.malicious.com";
    sid:9000002; rev:1;
)

# JA3 hash match for malware TLS client
alert tls $HOME_NET any -> $EXTERNAL_NET any (
    msg:"MALWARE MalwareX JA3 Match";
    ja3.hash; content:"a0e9f5d64349fb13191bc781f81f42e1";
    sid:9000003; rev:1;
)
EOF
```

### Step 6: Extract Files and Artifacts from Traffic

Recover transferred files and embedded data:

```bash
# Extract files using Zeek
zeek -r malware.pcap /opt/zeek/share/zeek/policy/frameworks/files/extract-all-files.zeek
ls extract_files/

# Extract files using NetworkMiner (GUI)
# Or use tshark for specific protocol exports
tshark -r malware.pcap --export-objects http,http_objects/
tshark -r malware.pcap --export-objects smb,smb_objects/
tshark -r malware.pcap --export-objects tftp,tftp_objects/

# Hash all extracted files
sha256sum http_objects/* smb_objects/* 2>/dev/null

# Generate Zeek logs for comprehensive metadata
zeek -r malware.pcap
# Output: conn.log, dns.log, http.log, ssl.log, files.log, etc.
```

## Key Concepts

| Term | Definition |
|------|------------|
| **Beaconing** | Regular periodic connections from malware to C2 server, identifiable by consistent time intervals and packet sizes |
| **JA3/JA3S** | TLS fingerprinting method creating a hash from ClientHello/ServerHello parameters to uniquely identify malware TLS implementations |
| **DGA (Domain Generation Algorithm)** | Algorithm generating pseudo-random domain names that malware queries to locate C2 servers, evading static domain blocklists |
| **DNS Tunneling** | Encoding data in DNS queries and responses to establish a C2 channel or exfiltrate data through DNS infrastructure |
| **Fast Flux** | DNS technique rapidly rotating IP addresses for a domain to avoid takedown and distribute C2 across many compromised hosts |
| **SNI (Server Name Indication)** | TLS extension revealing the hostname the client is connecting to; visible even in encrypted HTTPS connections |
| **Network Signature** | Suricata/Snort rule matching specific patterns in network traffic (headers, payloads, timing) to detect malicious communications |

## Tools & Systems

- **Wireshark**: Open-source