Introduction

When it comes to security assessments and penetration testing, one of the most critical steps is identifying open ports on a remote system. Open ports indicate the presence of services running on the target machine and can provide valuable information about the target system’s attack surface. In this article, we’ll be discussing remote port enumeration using native tools and how it can be used to assess the security of a target system.

What is remote port enumeration?

Remote port enumeration is the process of identifying open ports on a remote system. It can be used to gather information about the target system and identify potential vulnerabilities. By knowing which ports are open, an attacker can determine which services are running on the target machine and exploit any known vulnerabilities associated with those services.

Why use native tools?

Using native tools is often the simplest and most straightforward way to perform remote port enumeration. They are easy to use, don’t require any additional software installations, and are widely available on all major operating systems. Furthermore, native tools can be executed from the command line, making it easy to automate the process of port scanning.

Types of native tools

There are several native tools that can be used to perform remote port enumeration, including:

Telnet

Telnet is a network protocol that provides a command-line interface for remote communication. It can be used to establish a connection with a remote host and perform port scans. To perform a remote port scan using Telnet, the following command can be executed:

telnet target-system port

Nmap

Nmap is a free and open-source tool that is widely used for network discovery and security auditing. Nmap can be used to perform remote port scans, identify open ports, and gather information about the target system, such as the operating system, network topology, and running services. To perform a remote port scan using Nmap, the following command can be executed:

nmap target-system

Netstat

Netstat is a native tool that provides information about active connections, including open ports and active sockets. To perform a remote port scan using Netstat, the following command can be executed:

netstat -an

Fping

Fping is a native tool that can be used to ping multiple hosts simultaneously and determine which hosts are active. To perform a remote port scan using Fping, the following command can be executed:

fping -g target-range

Examples of remote port enumeration

Telnet

To demonstrate how to perform remote port enumeration using Telnet, we’ll be using a target system with the IP address 192.168.0.100. In this example, we’ll be attempting to establish a connection with the target system on port 80, which is the default port for HTTP. To perform the port scan, we’ll execute the following command:

telnet 192.168.0.100 80

If the connection is successful, Telnet will display a message indicating that the connection has been established. If the connection is unsuccessful, Telnet will display an error message indicating that the connection could not be established.

Nmap

To demonstrate how to perform remote port enumeration using Nmap, we’ll be using the same target system as in the previous example. In this example, we’ll be performing a full port scan of the target system to identify open ports. To perform the port scan, we’ll execute the following command:

nmap 192.168.0.100

Nmap will then perform a full port scan of the target system, identifying open ports and the services running on those ports. The output will show the target system’s IP address, the open ports, and the services running on those ports. The output will also show the operating system and the network topology of the target system.

Netstat

To demonstrate how to perform remote port enumeration using Netstat, we’ll be using the same target system as in the previous examples. In this example, we’ll be using the netstat command to identify open ports and active connections. To perform the port scan, we’ll execute the following command:

netstat -an

Netstat will then display information about the active connections, including the open ports and the state of the connections. The output will show the IP address of the target system, the open ports, and the state of the connections.

Fping

To demonstrate how to perform remote port enumeration using Fping, we’ll be using the same target system as in the previous examples. In this example, we’ll be using Fping to identify active hosts on a target range. To perform the port scan, we’ll execute the following command:

fping -g 192.168.0.0/24

Fping will then ping all hosts in the target range and determine which hosts are active. The output will show the IP address of the active hosts and the response time.

Conclusion

Remote port enumeration is a critical step in security assessments and penetration testing. By identifying open ports on a remote system, an attacker can determine the target system’s attack surface and identify potential vulnerabilities. Native tools, such as Telnet, Nmap, Netstat, and Fping, can be used to perform remote port enumeration and gather information about the target system. The examples provided in this article demonstrate how to perform remote port enumeration using these tools, but there are many other tools and techniques that can be used to perform remote port enumeration.