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// Other services

Port 1131: CAC App Service Protocol Encripted

Port 1131 is assigned by IANA to caspssl (CAC App Service Protocol Encripted).

1131

How caspssl works

Other services
client:1131caspsslresponse client:1131caspsslresponse

The client sends a request to port 1131 and the caspssl 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 1131 dangerous?

We have no specific security note for port 1131. 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 1131

ServicePortTransportDescriptionReferenceUpdated
caspssl 1131 TCP, UDP CAC App Service Protocol Encripted - 2006-02

// source: IANA service name and port number registry

03 Check it

Which program uses port 1131, and is it reachable?

Linux

sudo ss -ltnup 'sport = :1131'      # process listening on 1131
sudo lsof -nP -i :1131

macOS

sudo lsof -nP -i :1131

Windows (PowerShell)

Get-NetTCPConnection -LocalPort 1131 -State Listen | Select LocalAddress, OwningProcess
Get-NetUDPEndpoint -LocalPort 1131
netstat -ano | findstr :1131

From another machine

nmap -p 1131 -sV <host>
sudo nmap -sU -p 1131 <host>
nc -zv <host> 1131

Block it in the firewall

sudo ufw deny 1131/tcp                                         # Linux (ufw)
New-NetFirewallRule -DisplayName "Block 1131" -Direction Inbound -LocalPort 1131 -Protocol TCP -Action Block  # Windows
04 FAQ
What is port 1131 used for?

Port 1131 is assigned by IANA to caspssl (CAC App Service Protocol Encripted).

Is port 1131 TCP or UDP?

Port 1131 is registered for TCP and UDP.

Is it safe to open port 1131?

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 1131 is open?

On Linux run "ss -ltnup 'sport = :1131'", on macOS "lsof -nP -i :1131", and on Windows "netstat -ano | findstr :1131" to see the local process. From another machine, "nmap -p 1131 <host>" shows whether it is reachable.

05 Related
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