From cybersecurity-skills
Detects network scanning (Nmap, Masscan) using Suricata/Snort IDS signatures, threshold rules, and traffic anomaly analysis for early reconnaissance alerts.
npx claudepluginhub mukul975/anthropic-cybersecurity-skills --plugin cybersecurity-skillsThis skill uses the workspace's default tool permissions.
Network scanning is typically the first phase of an attack, where adversaries enumerate live hosts, open ports, running services, and OS versions using tools like Nmap, Masscan, ZMap, and custom scanners. Detecting this reconnaissance activity provides early warning of potential attacks. IDS/IPS systems like Suricata and Snort can identify scanning through signature-based detection (matching kn...
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Network scanning is typically the first phase of an attack, where adversaries enumerate live hosts, open ports, running services, and OS versions using tools like Nmap, Masscan, ZMap, and custom scanners. Detecting this reconnaissance activity provides early warning of potential attacks. IDS/IPS systems like Suricata and Snort can identify scanning through signature-based detection (matching known scanner packet patterns), threshold-based detection (counting connection attempts over time), and anomaly detection (identifying unusual traffic patterns). This skill covers writing and deploying IDS signatures for scan detection, configuring threshold-based alerting, and correlating scan activity with downstream attack indicators.
| Scan Type | Nmap Flag | Packet Characteristics | Detection Method |
|---|---|---|---|
| TCP SYN | -sS | SYN flag only, no completion | SYN without SYN/ACK response pattern |
| TCP Connect | -sT | Full 3-way handshake | Multiple connections from single source |
| TCP FIN | -sF | FIN flag only | FIN to closed port (RST response) |
| TCP Xmas | -sX | FIN+PSH+URG flags | Unusual flag combination |
| TCP NULL | -sN | No flags set | Zero-flag TCP packet |
| UDP Scan | -sU | UDP to many ports | ICMP port unreachable responses |
| ACK Scan | -sA | ACK flag only (firewall probing) | Unsolicited ACK packets |
| SYN/ACK Scan | Custom | SYN+ACK without prior SYN | State violation |
| OS Fingerprint | -O | Unusual TCP options/window sizes | Specific option combinations |
| Version Detect | -sV | Service probe strings | Known probe payloads |
| Template | Nmap Flag | Speed | Detection Difficulty |
|---|---|---|---|
| Paranoid | -T0 | 1 probe/5 min | Very difficult |
| Sneaky | -T1 | 1 probe/15 sec | Difficult |
| Polite | -T2 | 1 probe/0.4 sec | Moderate |
| Normal | -T3 | Default parallelism | Easy |
| Aggressive | -T4 | Parallel, 1.25s timeout | Very easy |
| Insane | -T5 | Maximum parallelism | Trivial |
Create /var/lib/suricata/rules/scan-detection.rules:
# === TCP Scan Detection ===
# Detect TCP SYN scan (high volume SYN without completion)
alert tcp $EXTERNAL_NET any -> $HOME_NET any (msg:"SCAN TCP SYN Scan Detected"; flags:S,12; threshold:type both,track by_src,count 30,seconds 10; classtype:attempted-recon; sid:5000001; rev:2;)
# Detect TCP FIN scan
alert tcp $EXTERNAL_NET any -> $HOME_NET any (msg:"SCAN TCP FIN Scan"; flags:F,12; threshold:type both,track by_src,count 20,seconds 60; classtype:attempted-recon; sid:5000002; rev:1;)
# Detect TCP Xmas scan (FIN+PSH+URG)
alert tcp $EXTERNAL_NET any -> $HOME_NET any (msg:"SCAN TCP Xmas Tree Scan"; flags:FPU,12; classtype:attempted-recon; sid:5000003; rev:1;)
# Detect TCP NULL scan (no flags)
alert tcp $EXTERNAL_NET any -> $HOME_NET any (msg:"SCAN TCP NULL Scan"; flags:0,12; classtype:attempted-recon; sid:5000004; rev:1;)
# Detect ACK scan (firewall probing)
alert tcp $EXTERNAL_NET any -> $HOME_NET any (msg:"SCAN TCP ACK Scan"; flags:A,12; flow:stateless; threshold:type both,track by_src,count 50,seconds 30; classtype:attempted-recon; sid:5000005; rev:1;)
# Detect SYN+ACK scan (unusual stateless probe)
alert tcp $EXTERNAL_NET any -> $HOME_NET any (msg:"SCAN TCP SYN-ACK Scan"; flags:SA,12; flow:stateless; threshold:type both,track by_src,count 30,seconds 30; classtype:attempted-recon; sid:5000006; rev:1;)
# === UDP Scan Detection ===
# Detect UDP port scan
alert udp $EXTERNAL_NET any -> $HOME_NET any (msg:"SCAN UDP Port Scan"; threshold:type both,track by_src,count 30,seconds 10; classtype:attempted-recon; sid:5000010; rev:1;)
# === Nmap Specific Detection ===
# Detect Nmap OS fingerprinting (T1 probe - ECN SYN)
alert tcp $EXTERNAL_NET any -> $HOME_NET any (msg:"SCAN Nmap OS Fingerprint Probe"; flags:SEC,12; window:1; classtype:attempted-recon; sid:5000020; rev:1;)
# Detect Nmap window scan (specific window size patterns)
alert tcp $EXTERNAL_NET any -> $HOME_NET any (msg:"SCAN Nmap Window Size Probe"; flags:A,12; flow:stateless; window:1024; threshold:type both,track by_src,count 10,seconds 30; classtype:attempted-recon; sid:5000021; rev:1;)
# Detect Nmap version detection probes
alert tcp $EXTERNAL_NET any -> $HOME_NET any (msg:"SCAN Nmap Service Version Probe"; flow:established; content:"HELP"; depth:4; threshold:type both,track by_src,count 5,seconds 60; classtype:attempted-recon; sid:5000022; rev:1;)
# Detect Nmap scripting engine (NSE)
alert http $EXTERNAL_NET any -> $HOME_NET any (msg:"SCAN Nmap NSE HTTP Script"; http.user_agent; content:"Nmap Scripting Engine"; classtype:attempted-recon; sid:5000023; rev:1;)
# === Masscan Detection ===
# Detect Masscan SYN scan (specific window size)
alert tcp $EXTERNAL_NET any -> $HOME_NET any (msg:"SCAN Masscan SYN Scan Detected"; flags:S,12; window:1024; threshold:type both,track by_src,count 100,seconds 10; classtype:attempted-recon; sid:5000030; rev:1;)
# === Internal Scan Detection ===
# Detect internal host scanning (lateral movement recon)
alert tcp $HOME_NET any -> $HOME_NET any (msg:"SCAN Internal Network Scan Detected"; flags:S,12; threshold:type both,track by_src,count 50,seconds 30; classtype:attempted-recon; sid:5000040; rev:1;)
# Detect internal ICMP sweep
alert icmp $HOME_NET any -> $HOME_NET any (msg:"SCAN Internal ICMP Sweep"; itype:8; threshold:type both,track by_src,count 30,seconds 10; classtype:attempted-recon; sid:5000041; rev:1;)
Edit /etc/suricata/threshold.config:
# Suppress scan alerts from authorized vulnerability scanners
suppress gen_id 1, sig_id 5000001, track by_src, ip 10.0.5.100
suppress gen_id 1, sig_id 5000001, track by_src, ip 10.0.5.101
# Rate-limit scan alerts to prevent log flooding
rate_filter gen_id 1, sig_id 5000001, track by_src, count 5, seconds 300, new_action alert, timeout 600
rate_filter gen_id 1, sig_id 5000040, track by_src, count 3, seconds 300, new_action alert, timeout 600
# Event filter for critical internal scans
event_filter gen_id 1, sig_id 5000040, type both, track by_src, count 1, seconds 60
#!/usr/bin/env python3
"""Analyze IDS alerts for network scanning activity and generate reports."""
import json
import sys
from collections import defaultdict
from datetime import datetime
class ScanDetector:
"""Correlate IDS alerts to identify scanning campaigns."""
def __init__(self):
self.scan_events = defaultdict(lambda: {
'source_ip': '',
'target_ips': set(),
'target_ports': set(),
'scan_types': set(),
'alert_count': 0,
'first_seen': None,
'last_seen': None,
'signatures': defaultdict(int),
})
def process_eve_json(self, filepath: str):
"""Process Suricata EVE JSON alert log."""
with open(filepath, 'r') as f:
for line in f:
try:
event = json.loads(line)
if event.get('event_type') != 'alert':
continue
alert = event.get('alert', {})
sig = alert.get('signature', '')
if 'SCAN' not in sig:
continue
src_ip = event.get('src_ip', '')
dst_ip = event.get('dest_ip', '')
dst_port = event.get('dest_port', 0)
ts = datetime.fromisoformat(
event['timestamp'].replace('Z', '+00:00')
)
scanner = self.scan_events[src_ip]
scanner['source_ip'] = src_ip
scanner['target_ips'].add(dst_ip)
scanner['target_ports'].add(dst_port)
scanner['alert_count'] += 1
scanner['signatures'][sig] += 1
if 'SYN' in sig:
scanner['scan_types'].add('SYN Scan')
elif 'FIN' in sig:
scanner['scan_types'].add('FIN Scan')
elif 'Xmas' in sig:
scanner['scan_types'].add('Xmas Scan')
elif 'NULL' in sig:
scanner['scan_types'].add('NULL Scan')
elif 'UDP' in sig:
scanner['scan_types'].add('UDP Scan')
elif 'Nmap' in sig:
scanner['scan_types'].add('Nmap Detected')
elif 'Masscan' in sig:
scanner['scan_types'].add('Masscan Detected')
elif 'Internal' in sig:
scanner['scan_types'].add('Internal Scan')
if scanner['first_seen'] is None or ts < scanner['first_seen']:
scanner['first_seen'] = ts
if scanner['last_seen'] is None or ts > scanner['last_seen']:
scanner['last_seen'] = ts
except (json.JSONDecodeError, KeyError, ValueError):
continue
def generate_report(self):
"""Generate scan detection report."""
scanners = sorted(
self.scan_events.values(),
key=lambda x: x['alert_count'],
reverse=True
)
print(f"\n{'='*70}")
print("NETWORK SCAN DETECTION REPORT")
print(f"{'='*70}")
print(f"Unique Scanning Sources: {len(scanners)}\n")
for scanner in scanners:
targets = len(scanner['target_ips'])
ports = len(scanner['target_ports'])
duration = (scanner['last_seen'] - scanner['first_seen']).total_seconds() \
if scanner['first_seen'] and scanner['last_seen'] else 0
is_internal = scanner['source_ip'].startswith(('10.', '172.', '192.168.'))
severity = "CRITICAL" if is_internal else \
"HIGH" if targets > 50 or ports > 100 else "MEDIUM"
print(f"[{severity}] Scanner: {scanner['source_ip']}")
print(f" Type: {'INTERNAL' if is_internal else 'EXTERNAL'}")
print(f" Scan Types: {', '.join(scanner['scan_types'])}")
print(f" Target Hosts: {targets}, Target Ports: {ports}")
print(f" Total Alerts: {scanner['alert_count']}")
print(f" Duration: {duration:.0f}s")
print(f" First Seen: {scanner['first_seen']}")
print(f" Top Signatures:")
for sig, count in sorted(
scanner['signatures'].items(), key=lambda x: x[1], reverse=True
)[:5]:
print(f" - {sig}: {count}")
print()
if __name__ == '__main__':
detector = ScanDetector()
log_file = sys.argv[1] if len(sys.argv) > 1 else '/var/log/suricata/eve.json'
detector.process_eve_json(log_file)
detector.generate_report()