Authentication

Telnet authenticates in cleartext with a username and password, and is attacked through vendor default credentials (rampant on devices), servers configured with no authentication or a direct shell, and brute force against the plaintext login. A valid login gives a terminal, often on network equipment or an embedded device with administrative scope.

1 min di letturaaggiornato il 7 ott 2026

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Telnet commonly carries its username/password exchange in plaintext unless an encryption extension is successfully negotiated. Authentication fails in three common ways: a device retains vendor defaults, a service requires no authentication and drops directly to a shell or menu, or an online password attack succeeds against weak credentials. A valid login yields a terminal whose privileges depend on the particular device and account.

bash

nc <target> 23        # try default/no-auth first
hydra -L users.txt -P passwords.txt telnet://<target> -t 4

Subtopics#

Default credentials: vendor and factory Telnet logins.
No authentication: servers that drop to a shell without a password.
Password brute force: online attacks against weak login credentials.

Authentication

Subtopics#

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