| name | hunting-for-domain-fronting-c2-traffic |
| description | Detect domain fronting C2 traffic by analyzing SNI vs HTTP Host header mismatches in proxy logs and TLS certificate discrepancies using pyOpenSSL for certificate inspection |
| domain | cybersecurity |
| subdomain | threat-hunting |
| tags | ["domain-fronting","c2-detection","tls-inspection","proxy-logs","pyopenssl","threat-hunting","network-security"] |
| version | 1.0 |
| author | mahipal |
| license | Apache-2.0 |
| d3fend_techniques | ["Application Protocol Command Analysis","Network Isolation","Network Traffic Analysis","Client-server Payload Profiling","Network Traffic Community Deviation"] |
| nist_csf | ["DE.CM-01","DE.AE-02","DE.AE-07","ID.RA-05"] |
| mitre_attack | ["T1046","T1057","T1082","T1083","T1071"] |
| source | https://github.com/mukul975/Anthropic-Cybersecurity-Skills |
| source_commit | 04450304b12645cb2b974ab96d28c0664758a88d |
Hunting for Domain Fronting C2 Traffic
Overview
Domain fronting (MITRE ATT&CK T1090.004) is a technique where attackers use different domain names in the TLS SNI field and the HTTP Host header to disguise C2 traffic behind legitimate CDN-hosted domains. This skill detects domain fronting by parsing proxy/web gateway logs for SNI-Host header mismatches, analyzing TLS certificates for CDN provider identification, flagging connections where the SNI points to a high-reputation domain but the Host header targets an attacker-controlled domain, and correlating with known CDN provider IP ranges.
When to Use
- When investigating security incidents that require hunting for domain fronting c2 traffic
- 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
- Web proxy or secure web gateway logs with SNI and Host header fields
- Python 3.8+ with pyOpenSSL and cryptography libraries
- TLS inspection enabled on proxy for Host header visibility
- CDN provider IP range lists (CloudFront, Azure CDN, Cloudflare)
Steps
- Parse proxy logs for connections with both SNI and Host header fields
- Compare SNI domain against HTTP Host header for mismatches
- Extract TLS certificate Subject and SAN fields using pyOpenSSL
- Identify CDN-hosted connections via certificate issuer and IP ranges
- Flag high-confidence domain fronting where SNI and Host differ on CDN IPs
- Score alerts based on domain reputation differential
- Generate detection report with network flow context
Expected Output
JSON report containing detected domain fronting indicators with SNI-Host pairs, certificate details, CDN provider identification, confidence scores, and MITRE ATT&CK technique mapping.
