Port 6623Kerberos V5 Telnet

Kerberos-authenticated Telnet service; session traffic is not encrypted unless Telnet encryption is separately negotiated.

inRemote Access

transport: tcp · udp
in transit: cleartext
assignment: official
risk: 2/10
lookups: 0

also known as ktelnet, Kerberos Telnet

Technical Details

what runs on :6623

Kerberos V5 Telnet is Telnet with Kerberos authentication, using Telnet's in-band option negotiation (RFC 854) and the Kerberos V5 authentication option (RFC 2942). Telnet sessions are stream-oriented and normally run over TCP; the registry also lists UDP for this service, but UDP is not the usual transport for an interactive Telnet session. Port 6623 is an assigned alternate service port; conventional Telnet commonly uses TCP/23. Kerberos authentication does not by itself encrypt the session data—Telnet encryption is a separate negotiated option.

Security Information

exposure of :6623

risk score

2/ 10safe

routine exposure. this port is rarely the way in on its own — keep it patched and logged and move on.

remote access averages 3.8 across 219 ports — this one sits 1.8 below.

in transit

cleartext

credentials and payloads are readable by anyone on path

assignment

official

registered with iana for this service — scanners fingerprint it by number

reachable over

tcp · udp

udp is connectionless — source addresses are trivially spoofed and it is a reflection favourite

security overview

Kerberos can provide strong authentication, but session contents may still travel in cleartext unless Telnet encryption is negotiated. Telnet is a legacy remote-access protocol and should not normally be exposed to the internet; prefer SSH. The assignment is obscure and has not appeared open in the cited Nmap scan data, so an unexpected listener on 6623 should be verified rather than assumed to be Kerberos Telnet.

Record

iana registry entry

port: :6623
service: Kerberos V5 Telnet
transport: TCPUDP
encryption: cleartext
assignment: iana registered
risk: 2/10safe
category: Remote Access
usage: IANA assigns TCP and UDP port 6623 to Telnet using Kerberos V5 authentication, registered to Robert J Scott in 2005. It is not a common default: ordinary Telnet uses TCP/23, and Nmap's internet-wide scan data has not observed 6623 open.
lookups: 0rank 993
added: 2026-10-11
updated: 2026-10-11
references: IANA service name registry — port 6623

Something wrong?

This record is maintained by the engineers who use port 6623. Every field on it is editable — change what's wrong, say how you know, and a reviewer publishes it, usually within a minute. Last touched 2026-10-11.

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edit this record →back to the registry

Related Ports

all 219 in remote access →

the 8 most looked-up other ports in remote access — 219 ports carry that label.

port	service	proto	category	risk	views
:8000	Intel Remote Desktop / Alternate HTTP Port	TCP	Web Services	safe	84.3k
:8888	D2GS Admin Console	TCP	Remote Access	caution	83.7k
:8881	Atlasz Secure Server	TCP	Web Services	caution	67.6k
:5938	TeamViewer	TCPUDP	Remote Access	caution	65.0k
:8291	Winbox MikroTik Admin	TCP	Security	caution	62.9k
:8008	IBM HTTP Server Admin	TCP	Web Services	caution	58.3k
:135	Microsoft EPMAP	TCPUDP	Security	caution	51.9k
:23	Telnet	TCP	Remote Access	caution	34.8k

risk mix of the 8 listed

safe13%
caution88%

0 of 8 encrypted

Port :6623Kerberos V5 Telnet

Technical Details

Security Information

Related Ports

Port 6623Kerberos V5 Telnet