Which of the following protocols is considered unsecured and should be avoided in a server environment?

In a server environment, Telnet is considered an unsecured protocol primarily because it transmits data, including sensitive information like usernames and passwords, in plaintext across the network. This lack of encryption makes it vulnerable to eavesdropping and man-in-the-middle attacks, where an attacker can easily intercept and read the traffic. Consequently, using Telnet can expose a server to significant security risks, as unauthorized parties could gain access to confidential data.

In contrast, protocols such as SSH (Secure Shell), SFTP (SSH File Transfer Protocol), and CHAP (Challenge Handshake Authentication Protocol) incorporate security measures such as encryption and secure authentication processes. SSH and SFTP specifically protect the data in transit by encrypting the communication, making them suitable for secure server environments. CHAP, while not primarily focused on secure communication, uses a challenge-response mechanism to securely authenticate users, adding another layer of security compared to unsecured methods like Telnet.

Therefore, in a secure server environment, it is essential to avoid using Telnet due to its inherent vulnerabilities.