CyberHunter
Local dataset, no network
// Other services

Port 9900: IUA

Port 9900 is assigned by IANA to iua (IUA).

9900

How iua works

Other services
client:9900iuaresponse client:9900iuaresponse

The client sends a request to port 9900 and the iua service answers.

Transport
TCP · UDP · SCTP
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
Other services
01 Security

Is port 9900 dangerous?

We have no specific security note for port 9900. Its risk depends on the program actually listening on it. General advice for other services services:

  • Close the port if nothing on the host needs it.
  • Identify the process that listens on it (commands below) before opening it in a firewall.
  • Expose a service only to the networks that use it.
02 Registry

IANA registry entries for port 9900

ServicePortTransportDescriptionReferenceUpdated
iua 9900 TCP, UDP, SCTP IUA - -

// source: IANA service name and port number registry

03 Check it

Which program uses port 9900, and is it reachable?

Linux

sudo ss -ltnup 'sport = :9900'      # process listening on 9900
sudo lsof -nP -i :9900

macOS

sudo lsof -nP -i :9900

Windows (PowerShell)

Get-NetTCPConnection -LocalPort 9900 -State Listen | Select LocalAddress, OwningProcess
Get-NetUDPEndpoint -LocalPort 9900
netstat -ano | findstr :9900

From another machine

nmap -p 9900 -sV <host>
sudo nmap -sU -p 9900 <host>
nc -zv <host> 9900

Block it in the firewall

sudo ufw deny 9900/tcp                                         # Linux (ufw)
New-NetFirewallRule -DisplayName "Block 9900" -Direction Inbound -LocalPort 9900 -Protocol TCP -Action Block  # Windows
04 FAQ
What is port 9900 used for?

Port 9900 is assigned by IANA to iua (IUA).

Is port 9900 TCP or UDP?

Port 9900 is registered for TCP and UDP and SCTP.

Is it safe to open port 9900?

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. Close the port if nothing on the host needs it.

How do I check if port 9900 is open?

On Linux run "ss -ltnup 'sport = :9900'", on macOS "lsof -nP -i :9900", and on Windows "netstat -ano | findstr :9900" to see the local process. From another machine, "nmap -p 9900 <host>" shows whether it is reachable.

05 Related
:4444 Metasploit default / krb524 tcp · udp · high risk :31337 Back Orifice / elite tcp · udp · high risk :1 TCP Port Service Multiplexer tcp · udp :5 Remote Job Entry tcp · udp :9 Discard tcp · udp · sctp · dccp :11 Active Users tcp · udp :17 Quote of the Day tcp · udp :18 Message Send Protocol (historic) tcp · udp

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