CyberHunter
Local dataset, no network
// Other services

Port 12121: NuPaper Session Service

Port 12121 is assigned by IANA to nupaper-ss (NuPaper Session Service).

12121

How nupaper-ss works

Other services
client:12121nupaper-ssresponse client:12121nupaper-ssresponse

The client sends a request to port 12121 and the nupaper-ss 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 12121 dangerous?

We have no specific security note for port 12121. 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 12121

ServicePortTransportDescriptionReferenceUpdated
nupaper-ss 12121 TCP, UDP NuPaper Session Service - 2005-11

// source: IANA service name and port number registry

03 Check it

Which program uses port 12121, and is it reachable?

Linux

sudo ss -ltnup 'sport = :12121'      # process listening on 12121
sudo lsof -nP -i :12121

macOS

sudo lsof -nP -i :12121

Windows (PowerShell)

Get-NetTCPConnection -LocalPort 12121 -State Listen | Select LocalAddress, OwningProcess
Get-NetUDPEndpoint -LocalPort 12121
netstat -ano | findstr :12121

From another machine

nmap -p 12121 -sV <host>
sudo nmap -sU -p 12121 <host>
nc -zv <host> 12121

Block it in the firewall

sudo ufw deny 12121/tcp                                         # Linux (ufw)
New-NetFirewallRule -DisplayName "Block 12121" -Direction Inbound -LocalPort 12121 -Protocol TCP -Action Block  # Windows
04 FAQ
What is port 12121 used for?

Port 12121 is assigned by IANA to nupaper-ss (NuPaper Session Service).

Is port 12121 TCP or UDP?

Port 12121 is registered for TCP and UDP.

Is it safe to open port 12121?

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 12121 is open?

On Linux run "ss -ltnup 'sport = :12121'", on macOS "lsof -nP -i :12121", and on Windows "netstat -ano | findstr :12121" to see the local process. From another machine, "nmap -p 12121 <host>" shows whether it is reachable.

05 Related
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