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Potential Protocol Tunneling via Cloudflared

Identifies the use of Cloudflare Tunnel (cloudflared) to expose a local service or create an outbound tunnel. Adversaries may abuse quick tunnels (e.g. tunnel --url http://127.0.0.1:80) or named tunnels to proxy C2 traffic or exfiltrate data through Cloudflare's edge while evading direct connection blocking.

Rule type: eql
Rule indices:

  • endgame-*
  • logs-crowdstrike.fdr*
  • logs-endpoint.events.process-*
  • logs-m365_defender.event-*
  • logs-sentinel_one_cloud_funnel.*
  • logs-system.security*
  • logs-windows.sysmon_operational-*
  • winlogbeat-*

Rule Severity: medium
Risk Score: 47
Runs every:
Searches indices from: now-9m
Maximum alerts per execution: 100
References:

Tags:

  • Domain: Endpoint
  • OS: Windows
  • Use Case: Threat Detection
  • Tactic: Command and Control
  • Resources: Investigation Guide
  • Data Source: Elastic Defend
  • Data Source: Sysmon
  • Data Source: SentinelOne
  • Data Source: Microsoft Defender for Endpoint
  • Data Source: Crowdstrike
  • Data Source: Elastic Endgame
  • Data Source: Windows Security Event Logs

Version: 1
Rule authors:

  • Elastic

Rule license: Elastic License v2

Cloudflare Tunnel (cloudflared) is a legitimate tool for exposing local services through Cloudflare's edge. Adversaries abuse it to create quick or named tunnels for C2, data exfiltration, or ingress tool transfer while evading direct connection blocking.

  • Confirm the process command line for tunnel, --url, or tunnel run to validate cloudflared tunnel usage.
  • Identify the parent process and process executable path; cloudflared run from temp or user writable locations is more suspicious than from Program Files.
  • For quick tunnel (--url http://...), identify the local URL and whether it could be a C2 callback or proxy.
  • Correlate with network data for outbound connections to Cloudflare IPs or trycloudflare.com-style hostnames around the same time.
  • Review the user and session that started the tunnel; look for other suspicious logon or execution from the same context.
  • Legitimate use of Cloudflare Tunnel for development or internal services may trigger this rule; consider allowlisting by path or user for approved use cases.
  • If unauthorized tunnel use is confirmed: isolate the host, terminate the cloudflared process, and block cloudflared or Cloudflare tunnel domains at DNS/firewall where policy permits.
  • Rotate credentials for any accounts that may have been exposed over the tunnel.
process where host.os.type == "windows" and event.type == "start" and
 (process.name : "cloudflared.exe" or ?process.pe.original_file_name == "cloudflared.exe" or ?process.code_signature.subject_name : "Cloudflare, Inc.") and process.args : "tunnel"

Framework: MITRE ATT&CK