Analyzing DNS Logs for Exfiltration
When to Use
Use this skill when:
- SOC teams suspect data exfiltration through DNS tunneling to bypass firewall/proxy controls
- Threat intelligence indicates adversaries using DNS-based C2 channels (e.g., Cobalt Strike DNS beacon)
- UEBA detects anomalous DNS query volumes from specific hosts
- Malware analysis reveals DNS-over-HTTPS (DoH) or DNS tunneling capabilities
Do not use for standard DNS troubleshooting or availability monitoring — this skill focuses on security-relevant DNS abuse detection.
Prerequisites
- DNS query logging enabled (Windows DNS Server, Bind, Infoblox, or Cisco Umbrella)
- DNS logs ingested into SIEM (Splunk with
Stream:DNS,dnssourcetype, or Zeek DNS logs) - Passive DNS data for historical domain resolution analysis
- Baseline of normal DNS behavior (query volume, domain distribution, TXT record frequency)
- Python with
mathandcollectionslibraries for entropy calculation
Workflow
Step 1: Detect DNS Tunneling via Subdomain Length Analysis
DNS tunneling encodes data in subdomain labels, creating unusually long queries:
index=dns sourcetype="stream:dns" query_type IN ("A", "A…
