Port 79 finger · TCP

What runs on port 79

The finger protocol returns information about a user: real name, login time, .plan file. It leaks exactly what an attacker wants (valid usernames) and was the vector of the 1988 Morris worm, so it is off everywhere except a few retro-computing hosts.

Software that uses it: fingerd · efingerd

Should port 79 be open?

Disable it. This is a legacy or insecure protocol. The recommendation is not to firewall it but to turn the service off and use the modern replacement.

• If a legacy system still runs it, block it at the perimeter at minimum.

Check port 79

# on the host: is anything listening, and which process?
ss -ltnp 'sport = :79'
sudo lsof -i :79

# from another machine: is it reachable?
nc -zv host 79
nmap -p 79 host
curl -v telnet://host:79      # raw TCP connect test, Ctrl-C to leave

A port that answers from the internet when it should not is the finding; nmap from a machine outside your network (or a VPS) is the honest test, because scans from inside the LAN pass the firewall you are trying to verify.

Allow or block port 79

# ufw (Ubuntu/Debian)
sudo ufw allow from 10.0.0.0/8 to any port 79 proto tcp
sudo ufw deny 79/tcp

# nftables
nft add rule inet filter input ip saddr 10.0.0.0/8 tcp dport 79 accept
nft add rule inet filter input tcp dport 79 drop

# iptables (legacy)
iptables -A INPUT -p tcp --dport 79 -s 10.0.0.0/8 -j ACCEPT
iptables -A INPUT -p tcp --dport 79 -j DROP

# firewalld
sudo firewall-cmd --permanent --add-rich-rule='rule family=ipv4 source address=10.0.0.0/8 port port=79 protocol=tcp accept'

Replace 10.0.0.0/8 with the networks that need access. Allowing by source address is the rule that matters; "allow 79" with no source is just "open".

Related ports

• 113 ident
• 70 Gopher
• 23 Telnet — Plaintext remote shell; should be off

Part of the port number reference. Ports are 16-bit numbers; see also the subnet calculator and the packet decoder, which shows ports inside TCP and UDP headers.

Questions