Individual skill
detecting-exfiltration-over-dns-with-zeek
Detect DNS-based data exfiltration by analyzing Zeek dns.log for high-entropy subdomains and anomalous query patterns
internal/tools/skills/data/network-security/detecting-exfiltration-over-dns-with-zeek/SKILL.md
Source commit d42f381ad34843e71a42658e5c57290c713e85af
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- Yes
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- Observed behavior
- Instructions only
- Last checked
- Nov 9, 2026
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Repository context
- Repository stars (not skill ratings)
- 1,319
- Repository last updated
- Nov 8, 2026
- License
- Apache-2.0
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- cybersecurity Repository topic
- security Repository topic
- bug-bounty Repository topic
- automation Repository topic
- autonomous-pentesting Repository topic
- ai-agent Repository topic
- ai-security Repository topic
- ethical-hacking Repository topic
- golang Repository topic
- penetration-testing Repository topic
- dns-exfiltration Declared skill tag
- zeek Declared skill tag
- entropy-analysis Declared skill tag
- threat-hunting Declared skill tag
- data Derived category
- security Derived category
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# Detecting Exfiltration over DNS with Zeek
## Overview
DNS tunneling and exfiltration is a technique used by attackers to bypass firewalls and DLP controls by encoding stolen data into DNS query subdomains. Legitimate DNS queries have predictable entropy and length patterns, while exfiltration queries contain encoded data with high Shannon entropy, unusually long subdomain labels, and high volumes of unique subdomains per parent domain.
This skill analyzes Zeek dns.log files (TSV format) to detect exfiltration indicators. The agent computes Shannon entropy for each subdomain component, identifies queries exceeding the 63-character DNS label limit, counts unique subdomains per parent domain, and flags domains that exceed configurable thresholds. These techniques detect tools like dnscat2, iodine, dns2tcp, and custom DNS tunneling implementations.
## When to Use
- When investigating security incidents that require detecting exfiltration over dns with zeek
- When building detection rules or threat hunting queries for this domain