CyberHunter
Local dataset, no network
// Gaming

Port 27015: Steam / Source engine

Source engine game servers and Steam.

27015

How Steam / Source engine works

Gaming
playergame serverposition, input, state × 60 / s playerserver60 updates / s

The game client and server exchange small updates many times per second over port 27015. It travels in clear text: anyone on the path can read it.

Transport
UDP · TCP
Exposure risk
3/10 moderate if reachable from the Internet
Encryption
Clear textreadable on the network
IANA status
Unassignedcommon use differs from the registry
Range
Registered (1024-49151)
Category
Gaming
01 Security

Is port 27015 dangerous?

Common attacks and weaknesses

  • Query amplification and DDoS.

How to secure it

  • Rate-limit queries and keep servers updated.

Unofficial use. The IANA assignment below differs from what is usually found on this port in practice.

02 Registry

IANA registry entries for port 27015

No entry. The port is free for any application, so check what uses it on your hosts.

// source: IANA service name and port number registry

03 Check it

Which program uses port 27015, and is it reachable?

Linux

sudo ss -ltnup 'sport = :27015'      # process listening on 27015
sudo lsof -nP -i :27015

macOS

sudo lsof -nP -i :27015

Windows (PowerShell)

Get-NetTCPConnection -LocalPort 27015 -State Listen | Select LocalAddress, OwningProcess
Get-NetUDPEndpoint -LocalPort 27015
netstat -ano | findstr :27015

From another machine

nmap -p 27015 -sV <host>
sudo nmap -sU -p 27015 <host>
nc -zv <host> 27015

Block it in the firewall

sudo ufw deny 27015/tcp                                         # Linux (ufw)
New-NetFirewallRule -DisplayName "Block 27015" -Direction Inbound -LocalPort 27015 -Protocol TCP -Action Block  # Windows
04 FAQ
What is port 27015 used for?

Source engine game servers and Steam.

Is port 27015 TCP or UDP?

Port 27015 is registered for UDP and TCP.

Is it safe to open port 27015?

It is rated 3/10 (moderate) when exposed to the Internet. Query amplification and DDoS. Rate-limit queries and keep servers updated.

How do I check if port 27015 is open?

On Linux run "ss -ltnup 'sport = :27015'", on macOS "lsof -nP -i :27015", and on Windows "netstat -ano | findstr :27015" to see the local process. From another machine, "nmap -p 27015 <host>" shows whether it is reachable.

05 Related
:25565 Minecraft tcp · moderate risk :666 doom Id Software tcp · udp :1926 Evolution Game Server tcp · udp :2346 Game Connection Port tcp · udp :2347 Game Announcement and Location tcp · udp :2348 Information to query for game status tcp · udp :2914 Game Lobby tcp · udp :3074 Xbox game port tcp · udp

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