What it does. Use Scapy to craft, send, sniff, and dissect TCP/UDP/ICMP/DNS packets, analyze pcap files, implement SYN scans, and detect anomalous traffic such as fragmented or malformed packets. Use when performing authorized network reconnaissance, protocol-level forensic analysis, or building traffic anomaly detection during security testing. Part of mukul975/Anthropic-Cybersecurity-Skills (817 security skills) (mukul975/Anthropic-Cybersecurity-Skills).

Install

• npx skills add mukul975/Anthropic-Cybersecurity-Skills --skill analyzing-network-packets-with-scapy, or copy the skill folder into ~/.claude/skills/analyzing-network-packets-with-scapy/.
• Raw file: curl -sL https://raw.githubusercontent.com/mukul975/Anthropic-Cybersecurity-Skills/HEAD/skills/analyzing-network-packets-with-scapy/SKILL.md

SKILL.md (verbatim)

name: analyzing-network-packets-with-scapy
description: Use Scapy to craft, send, sniff, and dissect TCP/UDP/ICMP/DNS packets, analyze pcap files, implement SYN scans, and detect anomalous traffic such as fragmented or malformed packets. Use when performing authorized network reconnaissance, protocol-level forensic analysis, or building traffic anomaly detection during security testing.
domain: cybersecurity
subdomain: network-security
tags:
- scapy
- packet-analysis
- network-forensics
- protocol-dissection
- pcap
- traffic-analysis
version: '1.0'
author: mahipal
license: Apache-2.0
nist_csf:
- PR.IR-01
- DE.CM-01
- ID.AM-03
- PR.DS-02
mitre_attack:
- T1040
- T1071
- T1046
- T1557

Analyzing Network Packets with Scapy

Overview

Scapy is a Python packet manipulation library that enables crafting, sending, sniffing, and dissecting network packets at granular protocol layers. This skill covers using Scapy for security-relevant tasks including TCP/UDP/ICMP packet crafting, pcap file analysis, protocol field extraction, SYN scan implementation, DNS query analysis, and detecting anomalous traffic patterns such as unusually fragmented packets or malformed headers.

When to Use

• When investigating security incidents that require analyzing network packets with scapy
• When building detection rules or threat hunting queries for this domain
• When SOC analysts need structured procedures for this analysis type
• When validating security monitoring coverage for related attack techniques

Prerequisites

• Python 3.8+ with scapy library installed (pip install scapy)
• Root/administrator privileges for raw socket operations (sniffing, sending)
• Npcap (Windows) or libpcap (Linux) for packet capture
• Authorization to perform packet operations on target network

Steps

1. Read and parse pcap/pcapng files with rdpcap() for offline analysis
2. Extract protocol layers (IP, TCP, UDP, DNS, HTTP) and field values
3. Compute traffic statistics: top talkers, protocol distribution, port frequency
4. Detect SYN flood patterns by analyzing TCP flag ratios
5. Identify DNS exfiltration indicators via query length and entropy analysis
6. Craft custom probe packets for authorized network testing
7. Export findings as structured JSON report

Expected Output

JSON report containing packet statistics, protocol distribution, top source/destination IPs, detected anomalies (SYN floods, DNS tunneling indicators, fragmentation attacks), and per-flow summaries.

Other files in this skill

• LICENSE
• references/api-reference.md
• scripts/agent.py

references/api-reference.md (verbatim)

Scapy Network Packet Analysis API Reference

Core Scapy Functions

Reading Packets

from scapy.all import rdpcap, sniff, wrpcap

# Read pcap file
packets = rdpcap("capture.pcap")

# Live sniff with BPF filter (requires root)
packets = sniff(filter="tcp port 80", count=100, iface="eth0")

# Write packets to pcap
wrpcap("output.pcap", packets)

Packet Layer Access

from scapy.all import IP, TCP, UDP, DNS, DNSQR, ICMP

pkt = packets[0]
pkt.haslayer(IP)        # Check if layer exists
pkt[IP].src             # Source IP
pkt[IP].dst             # Destination IP
pkt[TCP].sport          # Source port
pkt[TCP].dport          # Destination port
pkt[TCP].flags          # TCP flags: S, SA, A, FA, R, PA
pkt[DNS].qd.qname       # DNS query name
pkt[ICMP].type          # ICMP type (8=echo request, 0=echo reply)

Packet Crafting

from scapy.all import IP, TCP, sr1, send

# SYN probe (authorized testing only)
syn = IP(dst="192.168.1.1") / TCP(dport=80, flags="S")
response = sr1(syn, timeout=2, verbose=0)

# ICMP ping
ping = IP(dst="192.168.1.1") / ICMP()
send(ping, verbose=0)

# Custom DNS query
dns = IP(dst="8.8.8.8") / UDP(dport=53) / DNS(rd=1, qd=DNSQR(qname="example.com"))

Protocol Fields Reference

TCP Flags

ICMP Types

BPF Filter Syntax

tcp port 443              # TCP traffic on port 443
host 10.0.0.1             # All traffic to/from IP
src net 192.168.0.0/24    # Source from subnet
udp and port 53           # DNS traffic
tcp[tcpflags] & tcp-syn != 0  # SYN packets only

CLI Usage

# Analyze pcap file for anomalies
python agent.py --pcap capture.pcap --output report.json

# Custom thresholds
python agent.py --pcap traffic.pcapng --syn-threshold 50 --dns-length 30

# Port scan detection sensitivity
python agent.py --pcap scan.pcap --scan-threshold 10

Back to mukul975/Anthropic-Cybersecurity-Skills (817 security skills) or Agent skills.