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// Network services

Port 3861: winShadow Host Discovery

Port 3861 is assigned by IANA to winshadow-hd (winShadow Host Discovery).

3861

How winshadow-hd works

Network services
client:3861winshadow-hdresponse client:3861winshadow-hdresponse

The client sends a request to port 3861 and the winshadow-hd 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 3861 dangerous?

We have no specific security note for port 3861. 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 3861

ServicePortTransportDescriptionReferenceUpdated
winshadow-hd 3861 TCP, UDP winShadow Host Discovery - 2003-03

// source: IANA service name and port number registry

03 Check it

Which program uses port 3861, and is it reachable?

Linux

sudo ss -ltnup 'sport = :3861'      # process listening on 3861
sudo lsof -nP -i :3861

macOS

sudo lsof -nP -i :3861

Windows (PowerShell)

Get-NetTCPConnection -LocalPort 3861 -State Listen | Select LocalAddress, OwningProcess
Get-NetUDPEndpoint -LocalPort 3861
netstat -ano | findstr :3861

From another machine

nmap -p 3861 -sV <host>
sudo nmap -sU -p 3861 <host>
nc -zv <host> 3861

Block it in the firewall

sudo ufw deny 3861/tcp                                         # Linux (ufw)
New-NetFirewallRule -DisplayName "Block 3861" -Direction Inbound -LocalPort 3861 -Protocol TCP -Action Block  # Windows
04 FAQ
What is port 3861 used for?

Port 3861 is assigned by IANA to winshadow-hd (winShadow Host Discovery).

Is port 3861 TCP or UDP?

Port 3861 is registered for TCP and UDP.

Is it safe to open port 3861?

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 3861 is open?

On Linux run "ss -ltnup 'sport = :3861'", on macOS "lsof -nP -i :3861", and on Windows "netstat -ano | findstr :3861" to see the local process. From another machine, "nmap -p 3861 <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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