Port 992 – Telnet over TLS

TCP

Port 992 is the TLS-encrypted Telnet port. Standard Telnet on port 23 transmits everything in cleartext including passwords. Port 992 wraps the session in TLS encryption. In practice, SSH on port 22 replaced both Telnet variants entirely – port 992 exists in IANA but sees near-zero real deployment.

Port Number

992

Protocol

TCP

Service

Telnet SSL/TLS

Range

IANA Well-Known (0–1023)

Description

Telnet over TLS on port 992 was registered to provide encrypted terminal access without changing the Telnet protocol itself. The TLS layer wraps the entire session, protecting credentials and command output from eavesdropping. Port 992 never achieved meaningful adoption because SSH arrived at roughly the same time and provided superior security features – key-based authentication, integrity checking, port forwarding, and SFTP. The only environments where port 992 might appear are legacy network equipment management interfaces that added TLS support to their existing Telnet implementation rather than implementing SSH.

Security risks

1Entirely obsolete: no modern system implements Telnet over TLS on port 992. Any listener on this port is either misconfigured, a honeypot, or malware using an unusual port
2Telnet protocol weaknesses persist even with TLS: no key exchange verification UI, no host key pinning, and the Telnet option negotiation can be exploited
3False sense of security: even encrypted, Telnet lacks SSH features like key-based auth, agent forwarding, port forwarding, and proper session multiplexing
4If found running: indicates extremely outdated infrastructure that likely has far more serious security issues (unpatched OS, no key management, weak passwords)

Firewall guidance

Block port 992 unconditionally. There is no legitimate modern use case. If you find a service on port 992, investigate immediately – it may be malware using an uncommon port, or severely outdated equipment (some legacy network devices offered Telnet/TLS before SSH support was added).

Diagnosis commands

Check if anything is listening on port 992 (should be nothing)

shell

ss -tlnp | grep 992

Service detection on port 992 (identify what's actually running)

shell

nmap -sV -p 992 target

If something responds, check the TLS certificate for identification

shell

openssl s_client -connect target:992

Usage examples

Port 992 – Telnet over TLS

shell

openssl s_client -connect switch:992
nmap -p 992 target
telnet-ssl -z ssl host 992

Common services on this port

None in active use – SSH replaced this entirely

Related ports

Telnet (plaintext, dangerous)

SSH (the replacement for all Telnet variants)

992

Telnet/TLS (this port, never adopted)

History

Port 992 was registered with IANA for 'telnets' (Telnet over TLS) in the 1990s, alongside other 'secure' variants of plaintext protocols (HTTPS/443, IMAPS/993, POP3S/995). Unlike those, Telnet/TLS never gained traction because SSH (1995) provided a superior alternative with key-based authentication, port forwarding, and proper key exchange. No major Telnet client or server implemented port 992 widely. It remains an IANA registration with essentially zero real-world deployment.

FAQ

Is there any reason to use Telnet/TLS over SSH?

No. SSH is superior in every way: stronger authentication (public key, certificate-based), built-in key management, session multiplexing, port forwarding, SFTP/SCP file transfer, agent forwarding, and universal client/server availability. The only Telnet use case in 2024+ is accessing legacy network equipment that predates SSH support – and those devices don't support TLS either, so port 992 serves no one.