hunting-for-domain-fronting-c2-traffic

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. Use when detecting domain fronting c2 traffic by analyzing sni vs http.
domain	cybersecurity
subdomain	threat-hunting
tags	["domain-fronting","c2-detection","tls-inspection","proxy-logs","pyopenssl","threat-hunting","network-security"]
version	1.0
author	oyi77
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"]

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

Trigger phrases:

• "hunting for domain fronting c2 traffic"

• "Detect domain fronting C2 traffic by analyzing SNI vs HTTP Host header mismatche"

• 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

# Example: IOC detection
import re

IOC_PATTERNS = {
    "ip": r"\b(?:\d{1,3}\.){3}\d{1,3}\b",
    "domain": r"\b[a-z0-9-]+\.[a-z]{2,}\b",
    "hash_md5": r"\b[a-f0-9]{32}\b",
    "hash_sha256": r"\b[a-f0-9]{64}\b",
}

def extract_iocs(text: str) -> dict:
    return {k: re.findall(v, text) for k, v in IOC_PATTERNS.items()}

1. Parse proxy logs for connections with both SNI and Host header fields