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hunting-domain-fronting-and-cdn-abuse

Hunts for domain fronting and CDN abuse by detecting TLS SNI versus HTTP Host header mismatches and high-reputation CDN domains carrying anomalous traffic in network telemetry. Activates for requests to hunt domain fronting, detect SNI/Host mismatch, or find CDN abuse used to mask C2.

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Run score Not tested

See how to install

Files included (4)

  • SKILL.md2.5 KB
  • LICENSE340 B
  • references/api-reference.md1.1 KB
  • scripts/analyst.py2.7 KB

SKILL.md (original)

Review the instructions the agent will receive before you install.

Hunting Domain Fronting and CDN Abuse

When to Use

  • You have TLS/HTTP telemetry (Zeek ssl.log + http.log, proxy logs) and want to detect domain fronting, where the TLS SNI shows a benign CDN domain but the inner HTTP Host differs.
  • You are hunting C2 hidden behind high-reputation CDNs.

Do not use SNI/Host mismatch as definitive — some legitimate setups differ. Corroborate with destination behavior and reputation.

Prerequisites

  • Telemetry pairing TLS SNI with the inner HTTP Host (or proxy logs exposing both).

Workflow

Step 1: Detect SNI/Host mismatch

python scripts/analyst.py hunt flows.csv

Flags connections where the TLS SNI and HTTP Host headers resolve to different registered domains, especially when the SNI is a known CDN/fronting-capable domain.

Step 2: Surface CDN-hosted anomalies

Highlight high-reputation CDN SNIs carrying long-lived or beaconing flows.

Step 3: Confirm

Corroborate with beacon periodicity, JA3, and destination reputation; many CDN mismatches are benign.

Step 4: Operationalize

Write a detection for SNI/Host registered-domain mismatch on fronting-capable CDNs.

Validation

  • Mismatch is computed on the registered domain, not the full hostname.
  • Known CDN SNIs are recognized to prioritize fronting-capable cases.
  • Findings are presented with corroboration needs, not as proof.

Pitfalls

  • Legitimate multi-tenant CDN/edge configs producing benign mismatches.
  • Encrypted SNI (ECH) hiding the SNI entirely — different hunt required.
  • Treating any CDN traffic as suspicious (high false-positive rate).

References

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