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// Directory & authentication

Port 27999: TW Authentication/Key Distribution and

Port 27999 is assigned by IANA to tw-auth-key (TW Authentication/Key Distribution and).

27999

How tw-auth-key works

Directory & authentication
userdirectorytw-auth-keyresponse userdirectorytw-auth-keyresponse

The client proves who it is on port 27999 and gets an answer (or a ticket) it can use with other services.

Transport
TCP · UDP
Exposure risk
not rated depends on the program listening
Encryption
Unknownnot stated by the registry
IANA status
Assigned1 registered service
Range
Registered (1024-49151)
Category
Directory & authentication
01 Security

Is port 27999 dangerous?

We have no specific security note for port 27999. Its risk depends on the program actually listening on it. General advice for directory & authentication services:

  • Keep directory and authentication services on internal networks.
  • Require signing or TLS and disable anonymous queries.
  • Monitor authentication failures for spraying and brute force.
02 Registry

IANA registry entries for port 27999

ServicePortTransportDescriptionReferenceUpdated
tw-auth-key 27999 TCP, UDP TW Authentication/Key Distribution and - -

// source: IANA service name and port number registry

03 Check it

Which program uses port 27999, and is it reachable?

Linux

sudo ss -ltnup 'sport = :27999'      # process listening on 27999
sudo lsof -nP -i :27999

macOS

sudo lsof -nP -i :27999

Windows (PowerShell)

Get-NetTCPConnection -LocalPort 27999 -State Listen | Select LocalAddress, OwningProcess
Get-NetUDPEndpoint -LocalPort 27999
netstat -ano | findstr :27999

From another machine

nmap -p 27999 -sV <host>
sudo nmap -sU -p 27999 <host>
nc -zv <host> 27999

Block it in the firewall

sudo ufw deny 27999/tcp                                         # Linux (ufw)
New-NetFirewallRule -DisplayName "Block 27999" -Direction Inbound -LocalPort 27999 -Protocol TCP -Action Block  # Windows
04 FAQ
What is port 27999 used for?

Port 27999 is assigned by IANA to tw-auth-key (TW Authentication/Key Distribution and).

Is port 27999 TCP or UDP?

Port 27999 is registered for TCP and UDP.

Is it safe to open port 27999?

It depends on the program that listens on it. Open it only for a service you know and only to the networks that need it. Keep directory and authentication services on internal networks.

How do I check if port 27999 is open?

On Linux run "ss -ltnup 'sport = :27999'", on macOS "lsof -nP -i :27999", and on Windows "netstat -ano | findstr :27999" to see the local process. From another machine, "nmap -p 27999 <host>" shows whether it is reachable.

05 Related
:389 LDAP tcp · udp · high risk :636 LDAPS tcp · udp · moderate risk :88 Kerberos tcp · udp · high risk :3268 Global Catalog (LDAP) tcp · udp · high risk :1812 RADIUS udp · tcp · moderate risk :31 MSG Authentication tcp · udp :49 Login Host Protocol (TACACS) tcp · udp :56 XNS Authentication tcp · udp

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