Digging Tunnels – Hunting Adversarial Cloudflared Instances

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Cloudflare’s `cloudflared` is a powerful tunneling tool used to securely expose local services to the internet. However, adversaries abuse it for malicious purposes, such as C2 (Command and Control) communication, data exfiltration, or bypassing network restrictions. This article explores hunting adversarial `cloudflared` instances and provides actionable techniques to detect and mitigate such threats.

Read the full article here: https://sudorem.dev/digging-tunnels-hunting-adversarial-cloudflared-instances

You Should Know:

1. Detecting Suspicious `cloudflared` Processes

Use Linux commands to identify unauthorized `cloudflared` instances:

ps aux | grep cloudflared 
netstat -tulnp | grep cloudflared 
lsof -i :7844  Default cloudflared port

2. Monitoring Network Traffic

Check for unusual outbound connections:

tcpdump -i eth0 'dst port 7844' -w cloudflared_traffic.pcap 
tshark -i eth0 -Y "tcp.port == 7844"

3. Blocking Malicious Tunnels with Firewall Rules

iptables -A OUTPUT -p tcp --dport 7844 -j DROP 
ufw deny out 7844/tcp

4. Hunting in Windows Environments

Get-Process | Where-Object { $_.Name -like "cloudflared" } 
netstat -ano | findstr "7844"

5. Analyzing Logs for Anomalies

journalctl -u cloudflared --no-pager | grep "error|unauthorized" 
grep "cloudflared" /var/log/syslog

6. Using YARA for Detection

Create a YARA rule to detect malicious `cloudflared` configurations: 

rule Cloudflared_Malicious_Tunnel { 
meta: 
description = "Detects adversarial cloudflared tunnels" 
strings: 
$config = "tunnel: malicious-domain" 
condition: 
$config 
}
  1. Automated Hunting with SIEM (Splunk Query Example) 
    index=network sourcetype=firewall dest_port=7844 | stats count by src_ip

What Undercode Say:

Adversaries increasingly abuse legitimate tools like `cloudflared` for stealthy operations. Proactive monitoring, network segmentation, and behavioral analysis are critical. Implement strict egress filtering, enforce endpoint detection, and regularly audit tunnel configurations.

Expected Output:

2025-06-08 14:30:01 WARNING [bash] Unauthorized tunnel attempt from 192.168.1.100

Prediction:

As tunneling tools evolve, attackers will leverage more obfuscation techniques, requiring defenders to adopt machine learning-based anomaly detection and deeper protocol inspection.

Relevant URL:

Expected Output:

[+] Detected and blocked adversarial cloudflared tunnel on port 7844

IT/Security Reporter URL:

Reported By: Aleborges Digging – Hackers Feeds
Extra Hub: Undercode MoN
Basic Verification: Pass ✅

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