Menu

Individual skill

detecting-exfiltration-over-dns-with-zeek

0upvotes

Detect DNS-based data exfiltration by analyzing Zeek dns.log for high-entropy subdomains, oversized TXT/NULL records, and anomalous query volume or patterns. Use when investigating suspected DNS tunneling, covert C2 over DNS, or data exfiltration hidden in DNS queries against network traffic captured by Zeek.

skills/detecting-exfiltration-over-dns-with-zeek/SKILL.md

Read pinned source

Source commit 54a798831d2266a3ca61ce68a7acb80b81160d57

What was checked

Matches the observed repository HEAD
Yes
Scanner rules are current
Yes
Repository scan complete
No
Skill scan complete
No
Observed behavior
Network or broad shell
Last checked
Nov 9, 2026

These are observations at the recorded commit, not a guarantee of safety. Review the source before running it.

Install this skill

Choose an agent in your Stack or copy a command below. Commands fetch the pinned commit and copy only this skill directory. Existing destinations are refused. Copying a command does not install anything.

An install command is unavailable: current rules, complete repository and skill scans, an eligible behavior level and a permitted license are required.

Repository context

Repository stars (not skill ratings)
35,862
Repository last updated
Aug 31, 2026
License
Apache-2.0

Observed agent integration: No specific integration evidence. Standard SKILL.md installation does not imply verified compatibility.

Files and excerpt

File metadata and permitted, redacted excerpts come from the recorded scan. Source links are pinned to that commit.

Browse files
Read excerpt


# 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
Back to top