7/tcp/udp - Pentesting Echo

👉 Overview

👀 What ?

The Echo Protocol is a service in the Internet Protocol Suite defined in RFC 862. It operates on port 7 both in the TCP and UDP services. The protocol was originally designed for testing and measurement of round-trip times and network bandwidth.

🧐 Why ?

Understanding the Echo protocol is important for cybersecurity professionals and pentesters as it can be used as a vector for security attacks. Attackers can use this protocol to cause a Denial of Service (DoS) attack by causing an infinite loop between two Echo servers, known as an 'Echo Storm'. Therefore, it is crucial to understand this protocol to protect systems and networks effectively.

⛏️ How ?

To pentest the Echo protocol, start by scanning the network to identify any systems that have port 7 open. Tools such as Nmap can be used for this purpose. Once identified, you can then use various techniques to test the vulnerability of the system. For instance, you can try to cause an Echo Storm by sending a large amount of echo requests to the system. Always remember to carry out such tests in a controlled and legal environment.

⏳ When ?

The Echo Protocol has been a part of the Internet Protocol Suite since its inception in the 1980s. However, due to its potential for misuse, it is often disabled on modern systems. Despite this, it is still important to check for this potential vulnerability when conducting a pentest.

⚙️ Technical Explanations

The Echo Protocol is a part of the Internet Protocol Suite and operates on port 7 for both TCP and UDP services. It functions by sending back any data it receives, hence the name 'Echo'. This characteristic is useful for testing network communication and measuring round-trip time - the time it takes for data to travel to a specific destination and back.

However, this simplicity of the protocol makes it susceptible to misuse and potentially harmful cyber attacks. One such method is a Denial of Service (DoS) attack. In a DoS attack, an attacker overwhelms an Echo server by sending a large amount of data to it. The server then struggles to respond to legitimate requests due to the overload of data it's trying to echo back.

Another misuse of the Echo protocol is creating an 'Echo Storm'. In this scenario, an attacker manipulates two Echo servers to continuously send data back and forth to each other, creating an infinite loop. This not only overwhelms the servers involved but can also consume significant network bandwidth, leading to network congestion and potentially causing service disruptions.

To safeguard against these vulnerabilities, it is often recommended to disable the Echo service on modern systems. However, for cybersecurity professionals and pentesters, understanding these potential vulnerabilities and how to test for them is essential. Tools like Nmap can be used to scan networks and identify any systems that have port 7 open, indicating the Echo service might be active. Such tests should always be performed in a controlled and legal environment to avoid unintentional harm.

For example, let's say you're a cybersecurity professional conducting a pentest in a controlled environment. Here's how you might test for the Echo service.

Step 1: Scanning the network

You'll first need to identify any systems that have port 7 open. To do this, you can use the Nmap tool with the following command line:

nmap -p 7 192.168.1.0/24

In this command, -p 7 specifies that you're scanning for port 7, and 192.168.1.0/24 specifies the IP range of the network you're scanning.

Step 2: Interpreting the results

The output might look something like this:

Nmap scan report for 192.168.1.105
Port    State  Service
7/tcp   open   echo

In this case, the echo service is open on the system with the IP address 192.168.1.105.

Step 3: Testing the vulnerability

If you find a system with the Echo service open, you can then test its vulnerability. For this, you might use a tool such as hping3 to send a large amount of echo requests to the system:

hping3 -1 --flood -a 192.168.1.105 192.168.1.106

Here, -1 specifies that you're using ICMP echo requests, --flood sends packets as fast as possible, -a 192.168.1.105 spoofs the source IP to cause an Echo Storm, and 192.168.1.106 is the target IP.

Remember, always perform these tests in a controlled and legal environment to avoid causing unintentional harm.