What makes Telnet vulnerable?

CryptographySystem SecurityEthical Hacking

If you need to connect to a distant machine via the command line, you might be tempted to utilize Telnet, one of the oldest protocols still in use on the Internet. However, it would be best to do so because it compromises your digital privacy.

We'll go through why you shouldn't use Telnet to connect to servers remotely and what other safety protocols you may use instead.

What is Telnet?

Telnet (TN) is a networking protocol and software package that allows you to connect to remote computers and terminals through a TCP/IP network or the Internet. Telnet was created in 1969 and standardized by the Internet Engineering Task Force as one of the initial Internet protocols (IETF).

Telnet is a purpose-built program that connects a remote computer/server to a host computer. It was designed for remote server access, management, and client/server architectures. A user can access privileged functionality on a distant system by supplying correct login and sign-in credentials. Telnet commands can be run on any client or server device that supports Telnet.

Telnet does not have any security features and sends all messages clear text. As a result, Secure Shell has largely supplanted Telnet in many applications and services (SSH).

Working of Telnet

Telnet is a client-server protocol that can connect to a remote computer, usually a server, and open a command line. This utility can be used to ping a port and determine whether it is open. Telnet makes use of a virtual terminal connection emulator, which is an abstract instance of a computer connection that mimics a physical terminal connected to a system by using standard protocols. FTP and Telnet can be utilized together for users who need to communicate data files.

Telnet allows users to connect to a machine remotely, often known as Telnetting into the system. They must provide their login and password combination to gain access to the remote computer, which allows them to run command lines as if they were physically present at the computer. Users' IP addresses will match the computer they are signed in to rather than the one they used to log in, regardless of their physical location.

Security Concerns with Telnet

Telnet sessions between the client and the server are not encrypted without a workaround. Those who have access to the TCP/IP packet flow between hosts can monitor all traffic, listen in, and record potentially sensitive information such as logins and passwords of Telnet server users. Using Telnet, all content transferred between computers is in plain text. This also applies to usernames and passwords. If you're using Telnet, a "man-in-the-middle" attack can easily intercept the connection and reveal any credentials you send.

This illustrates the several cultures in which Arpanet, the initial network that evolved into the Internet, was created. Arpanet was an experimental US government research project in the late 1960s and early 1970s, with no plans to become the vast global network that the modern Internet is today.

The creators were academics who wanted to connect the country's leading research universities, and they had faith in one another. Nobody would ever attempt to break into a computer.

Some router manufacturers continue to utilize Telnet and leave it accessible and make other security mistakes, such as hardcoding credentials. It's reached the point where the attack strategy is becoming too predictable: infect a device, then seek additional devices on the same network with the Telnet protocol port open.

The malware will try some popular or default passwords in rare cases and hunt for other open ports. Taking control is easy if the hardware isn't adequately protected and still has an overly open port. Telnet uses port 23 on routers unless otherwise configured. However, it is not the only protocol that uses this port. Many other IoT devices use telnet, and it's risky because the communication isn't encrypted and is done in plain text. Telnet is considered an antiquated technology.

Telnet's Applications

Telnet can be used to do a range of tasks on a server, including file editing, program execution, and email checking.

Some servers allow remote access to public data via Telnet, allowing users to play simple games or look up weather forecasts. Many of these features exist because they are nostalgic or compatible with earlier systems requiring specific data.

Telnet also allows users to connect to any software that uses text-based, unencrypted protocols, such as web servers and ports. Users can type Telnet followed by the name or IP address of the remote device into a distant system's command prompt, and the telnet connection will ping the port to see if it is open or not. A blank screen indicates that the port is open but has an error message.

Alternates to Telnet: SSH and Mosh

Tatu Ylönen, then a student at Finland's Helsinki University of Technology, was inspired to build Secure Shell, or SSH, in response to a password-stealing attack. OpenSSH, an OpenBSD project, is one of the most extensively used security protocols on current Unix and Linux systems. Even Windows 10 comes with a built-in version of OpenSSH.

It's not unexpected, given that SSH eliminates the issue that made Telnet so dangerous in the first place. SSH is a protocol that encrypts connections between two or more machines, so even if an attacker manages to tap into it, they won't be able to decipher what's going on.

SSH, like Telnet, is extremely helpful, but the major technical assumptions that it was built on meant that further network deployments exposed its flaws. Wired, always-on connections are assumed in SSH. See what happens if you close your laptop lid while connected. Your SSH connection will become unresponsive.

SSH is a cryptographic protocol and interfaces for running network services, shell services, and secure network communication with a remote computer. On top of an unsecured network, Secure Shell allows two remotely connected users to perform network communication and other services. It was originally a Unix command, but it is also supported on Windows computers. SSH was created to allow a user to log on to a distant computer securely and conduct shell and network functions. For example, network administrators could use it to log into a distant Web server. It's also a safe alternative to the Telnet, RSH, and rexec protocols. SSH-based communications/processes often use a client/server design, with both a client and a server SSH.

The client is authenticated and connected securely, and it delivers encrypted commands to the server to be executed. Digital certificates based on RSA public-key cryptography authenticate both the client and the server. The encryption techniques used by SSH are AES, IDEA, and Blowfish.

Mosh was created to address the issues of utilizing SSH on laptops, mobile devices, and wireless connections. Mosh allows you to stay connected even if your Wi-Fi network goes down, as well as efficiently roam between multiple networks.

The State Synchronization Protocol is a new protocol used by Mosh (SSP). Traditional remote connection technologies such as Telnet and SSH are used. Under SSH, the server sends some bytes downstream to the client.

SSP adds a new layer to the mix. Both the server and the client use sequence numbers to track transmitted. When the server receives a sequence number that differs from the previous one, it recognizes that the client has switched connections. This means that moving from one Wi-Fi network to another, or from one Wi-Fi network to a mobile network, or from one Wi-Fi network to a wired connection, and so on, is simple.

Real-time character echo is another helpful function provided by Mosh. When using SSH, you may notice a delay between typing and seeing your text appear on the screen since the server echoes what you're typing back to you.

SSH vs. Telnet: What's the Difference?

  • When compared to Telnet, SSH is more secure.

  • Telnet sends data in plain text, whereas SSH encrypts it.

  • Telnet does not employ any authentication, but SSH uses a public key for authentication.

  • Compared to Telnet, SSH adds a little more burden on the bandwidth.

  • SSH has almost wholly replaced Telnet in practically all applications.

  • Both SSH and Telnet are used for the same purpose.

  • Finally, SSH clients (software that allows you to connect with an SSH server) are available for all major operating systems and tablet operating systems.

Updated on 15-Mar-2022 13:19:59