CyberHunter
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// Network services

Port 42509: CA discovery response

Port 42509 is assigned by IANA to candrp (CA discovery response).

42509

How candrp works

Network services
client:42509candrpresponse client:42509candrpresponse

The client sends a request to port 42509 and the candrp 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
Network services
01 Security

Is port 42509 dangerous?

We have no specific security note for port 42509. Its risk depends on the program actually listening on it. General advice for network services services:

  • Answer only the networks that need the service (no open resolvers, relays or reflectors).
  • UDP services can be abused for DDoS amplification: rate-limit or block them at the edge.
  • Disable legacy test services that have no use in production.
02 Registry

IANA registry entries for port 42509

ServicePortTransportDescriptionReferenceUpdated
candrp 42509 TCP, UDP CA discovery response - 2005-08

// source: IANA service name and port number registry

03 Check it

Which program uses port 42509, and is it reachable?

Linux

sudo ss -ltnup 'sport = :42509'      # process listening on 42509
sudo lsof -nP -i :42509

macOS

sudo lsof -nP -i :42509

Windows (PowerShell)

Get-NetTCPConnection -LocalPort 42509 -State Listen | Select LocalAddress, OwningProcess
Get-NetUDPEndpoint -LocalPort 42509
netstat -ano | findstr :42509

From another machine

nmap -p 42509 -sV <host>
sudo nmap -sU -p 42509 <host>
nc -zv <host> 42509

Block it in the firewall

sudo ufw deny 42509/tcp                                         # Linux (ufw)
New-NetFirewallRule -DisplayName "Block 42509" -Direction Inbound -LocalPort 42509 -Protocol TCP -Action Block  # Windows
04 FAQ
What is port 42509 used for?

Port 42509 is assigned by IANA to candrp (CA discovery response).

Is port 42509 TCP or UDP?

Port 42509 is registered for TCP and UDP.

Is it safe to open port 42509?

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. Answer only the networks that need the service (no open resolvers, relays or reflectors).

How do I check if port 42509 is open?

On Linux run "ss -ltnup 'sport = :42509'", on macOS "lsof -nP -i :42509", and on Windows "netstat -ano | findstr :42509" to see the local process. From another machine, "nmap -p 42509 <host>" shows whether it is reachable.

05 Related
:53 DNS tcp · udp · moderate risk :135 MS RPC tcp · udp · high risk :123 NTP udp · tcp · moderate risk :67 DHCP server udp · tcp · moderate risk :111 rpcbind tcp · udp · high risk :9100 Raw printing (JetDirect) tcp · udp · high risk :631 IPP / CUPS tcp · udp · high risk :5353 mDNS udp · tcp · moderate risk

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