CyberHunter
Local dataset, no network
// Other services

Port 20999: At Hand MMP

Port 20999 is assigned by IANA to athand-mmp (At Hand MMP).

20999

How athand-mmp works

Other services
client:20999athand-mmpresponse client:20999athand-mmpresponse

The client sends a request to port 20999 and the athand-mmp 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 20999 dangerous?

We have no specific security note for port 20999. 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 20999

ServicePortTransportDescriptionReferenceUpdated
athand-mmp 20999 TCP, UDP At Hand MMP - -

// source: IANA service name and port number registry

03 Check it

Which program uses port 20999, and is it reachable?

Linux

sudo ss -ltnup 'sport = :20999'      # process listening on 20999
sudo lsof -nP -i :20999

macOS

sudo lsof -nP -i :20999

Windows (PowerShell)

Get-NetTCPConnection -LocalPort 20999 -State Listen | Select LocalAddress, OwningProcess
Get-NetUDPEndpoint -LocalPort 20999
netstat -ano | findstr :20999

From another machine

nmap -p 20999 -sV <host>
sudo nmap -sU -p 20999 <host>
nc -zv <host> 20999

Block it in the firewall

sudo ufw deny 20999/tcp                                         # Linux (ufw)
New-NetFirewallRule -DisplayName "Block 20999" -Direction Inbound -LocalPort 20999 -Protocol TCP -Action Block  # Windows
04 FAQ
What is port 20999 used for?

Port 20999 is assigned by IANA to athand-mmp (At Hand MMP).

Is port 20999 TCP or UDP?

Port 20999 is registered for TCP and UDP.

Is it safe to open port 20999?

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 20999 is open?

On Linux run "ss -ltnup 'sport = :20999'", on macOS "lsof -nP -i :20999", and on Windows "netstat -ano | findstr :20999" to see the local process. From another machine, "nmap -p 20999 <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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