Port / TCP
6379Redis
Redis serves in-memory keys, caches, queues, and session stores.
If it is internet-facing: Finding 6379 open to the internet is a finding in its own right — it warrants an explanation, not just a rule.
Exposure
Localhost only
Transport
Encryption optional
Risk if public
High
Exposure verdict
Port 6379 should be bound to 127.0.0.1. Nothing outside the host needs to reach it, and binding to 0.0.0.0 is the single change that turns it into an incident.
Encryption is available but negotiated or configured rather than guaranteed. A client that does not insist on it will silently fall back to plaintext.
Registered with IANA on request, but bindable by any unprivileged user. Registration records intent — it does not reserve the port, so collisions between products are common.
Grouped with the other databases & caches ports so a rule written for one can be checked against its neighbours.
What actually goes wrong
2 notes- Without a password, CONFIG SET can write files as the Redis user — a documented path from open port to remote code execution.
- Protected mode only helps until someone binds to 0.0.0.0; set requirepass and keep it on loopback or a private network.
Recommended firewall rule
Deny at the edge and bind to loopback
A firewall rule is the second line here. Fix the bind address in the service configuration so the listener never leaves the host.
ufw
sudo ufw deny 6379/tcpiptables
sudo iptables -A INPUT -p tcp --dport 6379 -j DROPIf you do need it open to everyone
sudo ufw allow 6379/tcpWrite down why. An unexplained allow rule outlives the person who added it, and the next reviewer has no way to tell a deliberate exception from an accident.
Check what is really there
Listening locally
sudo ss -tlpn 'sport = :6379'The bind address is the answer that matters: 127.0.0.1 is local-only, 0.0.0.0 and :: mean every interface.
Listening (macOS)
sudo lsof -nP -iTCP:6379 -sTCP:LISTENmacOS ships lsof rather than ss; this names the owning process and user.
From outside
nmap -sV -Pn -p 6379 <host>A version probe confirms whether Redis is actually what answers, rather than trusting the number. Only scan hosts you are authorised to test.
Reachability
nc -vz <host> 6379The quick yes/no when you only need to know whether a path exists through the firewall.