seikaikyo/hunting-for-domain-fronting-c2-traffic
external/anthropic-cybersecurity-skills/skills/hunting-for-domain-fronting-c2-traffic/SKILL.md
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.
$ install --global
skillsauthnpx skillsauth add seikaikyo/dash-skills hunting-for-domain-fronting-c2-trafficInstall this skill globally with one command. Works with Claude Code, Cursor, and Windsurf.
Security Scan Results
3 of 9 scanners reported clean
Some scanners were skipped, did not run, or reported a non-clean status. Review each row below.
3
Scanners Passed
9
Scanners in report
Clean
TrivyContainer and dependency vulnerability scanner
95%
Clean
SemgrepStatic code analysis for vulnerabilities
95%
Clean
mcp-scan (Snyk)Model Context Protocol security validation
95%
Skipped
Snyk (dep)Open source security scanning
50%
Skipped
Socket.devSupply chain security analysis
50%
Skipped
VirusTotalMulti-engine malware detection
50%
Skipped
CrowdStrikeAdvanced threat intelligence
50%
Skipped
OSV-ScannerOpen Source Vulnerability database check
50%
Skipped
OWASP Dep-Check
50%
Last scanned: Aug 14, 2026, 3:54 AM148.6s3 files scanned
SKILL.md
- name:
- hunting-for-domain-fronting-c2-traffic
- description:
- Detects domain fronting C2 traffic by analyzing SNI-vs-HTTP-Host-header
- domain:
- cybersecurity
- subdomain:
- threat-hunting
- version:
- 1.0
- author:
- mahipal
- license:
- Apache-2.0
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.
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