Port 5938 (TeamViewer)

TeamViewer's preferred connection port (it falls back to 443 and 80).

Registered (user) port, 1024-49151 TCPUDP Remote access Do not expose to the internet

What port 5938 is used for

TeamViewer's preferred connection port (it falls back to 443 and 80).

Security: should port 5938 be open?

Do not expose to the internet. Only outbound is needed. Blocking it does not stop TeamViewer since it falls back to 443; control it via policy instead.

IANA assignment

Port 5938 is in the registered range and has no IANA assignment. The usage above is unofficial but widespread.

Check what is listening on port 5938

Linux: is anything listening on TCP 5938?

sudo ss -tlnp 'sport = :5938'

Linux: UDP 5938

sudo ss -ulnp 'sport = :5938'

Linux / macOS: which process owns the port

sudo lsof -nP -i :5938

Older Linux / BSD (net-tools)

sudo netstat -tlnp | grep ':5938 '

Windows (Command Prompt)

netstat -ano | findstr :5938

Windows (PowerShell)

Get-NetTCPConnection -LocalPort 5938 -State Listen | Select LocalAddress,OwningProcess

Test it from outside

From another machine

nc -vz -w 5 HOST 5938

From Windows

Test-NetConnection HOST -Port 5938

UDP probe (no reply does not prove it is closed)

nc -vzu -w 5 HOST 5938

Block port 5938 in the firewall

ufw

sudo ufw deny 5938/tcp

iptables

sudo iptables -A INPUT -p tcp --dport 5938 -j DROP

nftables

sudo nft add rule inet filter input tcp dport 5938 drop

Windows Firewall

New-NetFirewallRule -DisplayName 'Block TCP 5938' -Direction Inbound -Protocol TCP -LocalPort 5938 -Action Block

ufw

sudo ufw deny 5938/udp