external/anthropic-cybersecurity-skills/skills/performing-dns-tunneling-detection/SKILL.md
Detects DNS tunneling by computing Shannon entropy of DNS query names, analyzing query length distributions, inspecting TXT record payloads, and identifying high subdomain cardinality. Uses scapy for packet capture analysis and statistical methods to distinguish legitimate DNS from covert channels. Use when hunting for data exfiltration.
npx skillsauth add seikaikyo/dash-skills performing-dns-tunneling-detectionInstall this skill globally with one command. Works with Claude Code, Cursor, and Windsurf.
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Analyze DNS traffic for indicators of DNS tunneling using entropy analysis and statistical methods on query name characteristics.
import math
from collections import Counter
def shannon_entropy(data):
if not data:
return 0
counter = Counter(data)
length = len(data)
return -sum((c/length) * math.log2(c/length) for c in counter.values())
# Legitimate domain: low entropy (~3.0-3.5)
print(shannon_entropy("www.google.com"))
# DNS tunnel: high entropy (~4.0-5.0)
print(shannon_entropy("aGVsbG8gd29ybGQ.tunnel.example.com"))
Key detection indicators:
from scapy.all import rdpcap, DNS, DNSQR
packets = rdpcap("dns_traffic.pcap")
for pkt in packets:
if pkt.haslayer(DNSQR):
query = pkt[DNSQR].qname.decode()
entropy = shannon_entropy(query)
if entropy > 4.0:
print(f"Suspicious: {query} (entropy={entropy:.2f})")
tools
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development
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testing
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