About

Imported from mukul975/anthropic-cybersecurity-skills (skills/hunting-for-domain-fronting-c2-traffic/SKILL.md). Install upstream with npx skills add mukul975/anthropic-cybersecurity-skills --skill hunting-for-domain-fronting-c2-traffic. Copyright stays with the author (Apache-2.0).

Hunting for Domain Fronting C2 Traffic

Name: hunting-for-domain-fronting-c2-traffic
Author: mukul975

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.

Use it

Copy one of these into your project. Installing also returns the manifest and these snippets.

yaml

targets:
  - https://api.opensmartroute.ai/api/v1/registry/mukul975-anthropic-cybersecurity-skills-hunting-for-doma-c08424/manifest   # or paste the manifest below

Manifest

An Open Capability Manifest: the router reads it to know what this does, what it costs and when to pick it.

mukul975-anthropic-cybersecurity-skills-hunting-for-doma-c08424.ocm.jsonjson

{
  "ocm": "1",
  "id": "mukul975-anthropic-cybersecurity-skills-hunting-for-doma-c08424",
  "kind": "skill",
  "name": "hunting-for-domain-fronting-c2-traffic",
  "description": "Detects domain fronting C2 traffic by analyzing SNI-vs-HTTP-Host-header mismatches in proxy logs and inspecting TLS certificate discrepancies with pyOpenSSL. Use when hunting for command-and-control traffic hidden behind legitimate CDN domains, or when investigating proxy/TLS logs for signs of domain fronting evasion.",
  "publisher": "mukul975",
  "version": "1.0.0",
  "capabilities": {
    "domains": [
      "general"
    ],
    "tags": [
      "skill-md",
      "domain-fronting",
      "c2-detection",
      "tls-inspection",
      "proxy-logs",
      "pyopenssl",
      "threat-hunting",
      "network-security",
      "skills-sh"
    ],
    "languages": [
      "en"
    ]
  },
  "quality_prior": 0.6,
  "examples": [
    "Detects domain fronting C2 traffic by analyzing SNI-vs-HTTP-Host-header mismatches in proxy logs and inspecting TLS certificate discrepancies with pyOpenSSL. Use when hunting for command-and-control traffic hidden behind legitimate CDN domains, or when investigating proxy/TLS logs for signs of domain fronting evasion."
  ],
  "primary": false,
  "metadata": {
    "source": {
      "provider": "skills.sh",
      "repository": "https://github.com/mukul975/anthropic-cybersecurity-skills",
      "path": "skills/hunting-for-domain-fronting-c2-traffic/SKILL.md",
      "ref": "HEAD",
      "url": "https://github.com/mukul975/anthropic-cybersecurity-skills/blob/HEAD/skills/hunting-for-domain-fronting-c2-traffic/SKILL.md",
      "key": "mukul975/anthropic-cybersecurity-skills/skills/hunting-for-domain-fronting-c2-traffic/SKILL.md"
    },
    "license": "Apache-2.0"
  },
  "instructions": "# Hunting for Domain Fronting C2 Traffic\n\n## Overview\n\nDomain 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",
  "cost": {
    "context_tokens": 470
  }
}

Fetch it by URL: GET /api/v1/registry/mukul975-anthropic-cybersecurity-skills-hunting-for-doma-c08424/manifest?version=1.0.0

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