CyberHunter
Local dataset, no network
// Other services

Port 9991: OSM Event Server

Port 9991 is assigned by IANA to osm-oev (OSM Event Server).

9991

How osm-oev works

Other services
client:9991osm-oevresponse client:9991osm-oevresponse

The client sends a request to port 9991 and the osm-oev service answers.

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
Other services
01 Security

Is port 9991 dangerous?

We have no specific security note for port 9991. 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 9991

ServicePortTransportDescriptionReferenceUpdated
osm-oev 9991 TCP, UDP OSM Event Server - 2003-08

// source: IANA service name and port number registry

03 Check it

Which program uses port 9991, and is it reachable?

Linux

sudo ss -ltnup 'sport = :9991'      # process listening on 9991
sudo lsof -nP -i :9991

macOS

sudo lsof -nP -i :9991

Windows (PowerShell)

Get-NetTCPConnection -LocalPort 9991 -State Listen | Select LocalAddress, OwningProcess
Get-NetUDPEndpoint -LocalPort 9991
netstat -ano | findstr :9991

From another machine

nmap -p 9991 -sV <host>
sudo nmap -sU -p 9991 <host>
nc -zv <host> 9991

Block it in the firewall

sudo ufw deny 9991/tcp                                         # Linux (ufw)
New-NetFirewallRule -DisplayName "Block 9991" -Direction Inbound -LocalPort 9991 -Protocol TCP -Action Block  # Windows
04 FAQ
What is port 9991 used for?

Port 9991 is assigned by IANA to osm-oev (OSM Event Server).

Is port 9991 TCP or UDP?

Port 9991 is registered for TCP and UDP.

Is it safe to open port 9991?

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 9991 is open?

On Linux run "ss -ltnup 'sport = :9991'", on macOS "lsof -nP -i :9991", and on Windows "netstat -ano | findstr :9991" to see the local process. From another machine, "nmap -p 9991 <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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