When Telnet was initially developed in 1969, most users of networked computers were in the computer departments of academic institutions, or at large private and government research facilities. In this environment, security was not nearly as much of a concern as it became after the bandwidth explosion of the 1990s. The rise in the number of people with access to the Internet, and by extension, the number of people attempting to crack other people's servers made encrypted alternatives much more of a necessity.
Experts in computer security, such as SANS Institute, and the members of the comp.os.linux.security newsgroup recommend that the use of Telnet for remote logins should be discontinued under all normal circumstances, for the following reasons:
* Telnet, by default, does not encrypt any data sent over the connection (including passwords), and so it is often practical to eavesdrop on the communications and use the password later for malicious purposes; anybody who has access to a router, switch, hub or gateway located on the network between the two hosts where Telnet is being used can intercept the packets passing by and obtain login and password information (and whatever else is typed) with any of several common utilities like tcpdump and Wireshark.
* Most implementations of Telnet have no authentication to ensure that communication is carried out between the two desired hosts and not intercepted in the middle.
* Commonly used Telnet daemons have several vulnerabilities discovered over the years.
These security-related shortcomings have seen the usage of the Telnet protocol drop rapidly, especially on the public Internet, in favor of the ssh protocol, first released in 1995. SSH provides much of the functionality of telnet, with the addition of strong encryption to prevent sensitive data such as passwords from being intercepted, and public key authentication, to ensure that the remote computer is actually who it claims to be.
As has happened with other early Internet protocols, extensions to the Telnet protocol provide TLS security and SASL authentication that address the above issues. However, most Telnet implementations do not support these extensions; and there has been relatively little interest in implementing these as SSH is adequate for most purposes. The main advantage of TLS-Telnet would be the ability to use certificate-authority signed server certificates to authenticate a server host to a client that does not yet have the server key stored. In SSH, there is a weakness in that the user must trust the first session to a host when it has not yet acquired the server key.
Experts in computer security, such as SANS Institute, and the members of the comp.os.linux.security newsgroup recommend that the use of Telnet for remote logins should be discontinued under all normal circumstances, for the following reasons:
* Telnet, by default, does not encrypt any data sent over the connection (including passwords), and so it is often practical to eavesdrop on the communications and use the password later for malicious purposes; anybody who has access to a router, switch, hub or gateway located on the network between the two hosts where Telnet is being used can intercept the packets passing by and obtain login and password information (and whatever else is typed) with any of several common utilities like tcpdump and Wireshark.
* Most implementations of Telnet have no authentication to ensure that communication is carried out between the two desired hosts and not intercepted in the middle.
* Commonly used Telnet daemons have several vulnerabilities discovered over the years.
These security-related shortcomings have seen the usage of the Telnet protocol drop rapidly, especially on the public Internet, in favor of the ssh protocol, first released in 1995. SSH provides much of the functionality of telnet, with the addition of strong encryption to prevent sensitive data such as passwords from being intercepted, and public key authentication, to ensure that the remote computer is actually who it claims to be.
As has happened with other early Internet protocols, extensions to the Telnet protocol provide TLS security and SASL authentication that address the above issues. However, most Telnet implementations do not support these extensions; and there has been relatively little interest in implementing these as SSH is adequate for most purposes. The main advantage of TLS-Telnet would be the ability to use certificate-authority signed server certificates to authenticate a server host to a client that does not yet have the server key stored. In SSH, there is a weakness in that the user must trust the first session to a host when it has not yet acquired the server key.
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