Which transport legacy protocol allows unsecure remote access to manage a network device?

The correct answer is Telnet. This protocol allows users to access network devices remotely in an unsecured manner. Telnet operates over TCP and provides a command-line interface for managing devices but lacks encryption, which means that any data transmitted over a Telnet session, including usernames and passwords, can be easily intercepted by attackers. This makes it unsuitable for secure management of network devices.

Although HTTP is also an unsecured protocol for web traffic, it is primarily designed for transferring web pages and data rather than for managing network devices. SSH, in contrast, is a secure protocol that encrypts all traffic, making it far more secure than Telnet. FTP is used for transferring files and does not focus on remote management of network devices.