BRev Port 6379 — Redis
Redis is an in-memory data store that was explicitly designed to run in a trusted network — the documentation says so — and until recently shipped with no authentication at all. Reaching port 6379 was, by default, full read and write access to every key, and that assumption is baked into an enormous amount of deployed configuration and tutorial copy.
The escalation from “open cache” to “owned host” is the part people underestimate. Because Redis can write its dataset to an arbitrary path with CONFIG SET dir and dbfilename, an attacker with write access can drop a crontab into /var/spool/cron, or an SSH public key into a user’s authorized_keys, and get command execution. Module loading widens it further. This is why our reference is unambiguous: never expose it.
Modern versions do help. Protected mode refuses commands from non-loopback clients when no password and no explicit bind are configured, and Redis 6 added ACLs and real users. But protected mode switches itself off the moment someone sets a bind address or a password, so it protects the untouched default and not the half-configured install — which is the one that ends up on the internet. Bind to 127.0.0.1, require a strong password, and rename or disable CONFIG.
Port 6379 at a glance
| Field | Value | Detail |
|---|---|---|
| Port | 6379 | Registered |
| Service | Redis | Redis in-memory data store. (TCP) |
| Category | Databases | data stores and their wire protocols |
| Exposure | Never | Never expose to the internet |
Should port 6379 face the internet? Never — the default configuration has no authentication, and a writable Redis can be turned into remote code execution (cron/SSH key injection). Bind to 127.0.0.1.
Bind it to localhost or a private network. Mass scanners find these within minutes of a host appearing online.
What commonly goes wrong
“DENIED Redis is running in protected mode”
The safety net working: Redis has no password and no explicit bind, so it refuses remote clients. The right response is to configure it properly — set requirepass and bind to the interface the application actually uses — not to disable protected mode, which is what most search results suggest and which is how instances end up open.
Unknown keys appear, or the instance is full of odd data
Treat it as a compromise, not a bug. Automated tooling writes marker keys and attempts the cron and SSH-key tricks described above. Check crontabs, authorized_keys files and running processes on the host, rotate anything the cache held, and rebuild if you find evidence of execution — then close the port before restoring.
Check port 6379 yourself
No browser can open a raw TCP socket, so no web page can honestly tell you whether this port is open on a remote host. These are the real commands, generated for port 6379 — swap example.com for the host you are actually testing.
Is port 6379 reachable on another host?
nc -vz example.com 6379"succeeded!" means the TCP handshake completed — the port is open. "Connection refused" is closed; a hang until timeout means filtered (a firewall dropped it silently).
nmap -Pn -p 6379 example.comThe only common tool that distinguishes open / closed / filtered. -Pn skips the ping sweep, so it still works against hosts that ignore ICMP.
Test-NetConnection example.com -Port 6379Read TcpTestSucceeded: True = open. It is built in — nothing to install.
telnet example.com 6379A blank screen or a banner means it connected. "Connection refused" means closed. Quit with Ctrl-] then `quit`.
curl -v --max-time 5 telnet://example.com:6379Handy when telnet is not installed: "Connected to …" proves the TCP handshake, without curl trying to speak HTTP.
What on this machine is holding port 6379?
sudo ss -tlnp | grep :6379Lists the listening socket and the PID/program holding it. Drop sudo and you get the socket but not the process name.
sudo lsof -i :6379The macOS answer to "address already in use". Kill it with `kill -9 <PID>` once you are sure what it is.
netstat -ano | findstr :6379The last column is the PID. Match it in Task Manager’s Details tab, or `taskkill /PID <pid> /F`.
No web page can tell you whether a port is open on a remote host
A browser cannot open a raw TCP socket — there is no API for it, by design. So a site that reports “port 3389 is OPEN on 203.0.113.10” is not checking from your browser; it is asking its own server to scan on your behalf. That works, but it means their server sees the host you asked about, scans from their address rather than yours, and answers a question about their network path, not yours.
We don't have a server here and won't pretend to. So this page does three honest things instead:
| Port | Proto | Service | What it is | Exposure | |
|---|---|---|---|---|---|
| 6379 | tcp | Redis | Redis in-memory data store.Never — the default configuration has no authentication, and a writable Redis can be turned into remote code execution (cron/SSH key injection). Bind to 127.0.0.1. | Never |
http://host:port/ and times it. A connection that is established proves a socket is open; an instant refusal usually means nothing is listening; anything else is honestly reported as “can't tell”. Each attempt gives up after 2.5s.nc -vz example.com 443
nmap -Pn -p 443 example.com
telnet example.com 443
curl -v --max-time 5 telnet://example.com:443
This page cannot answer that, and neither can any other page — from your browser. Opening a TCP connection to an arbitrary host and port is not something JavaScript is allowed to do. Every “open port checker” that gives you a green tick is running the scan on their server. Which is fine, as long as you know what you are agreeing to: they learn which host and port you were worried about, and the answer they give you is about the route from their data centre — not from the internet as your users see it.
What to do instead
Run the check from outside your own network. Copy an nmap or nc line from the card above and run it from a machine that is not behind the same router — a phone on mobile data with a terminal app, a cheap VPS, a colleague's laptop. Running it from inside the LAN tests the LAN, not the internet, and will happily say “open” while the world sees nothing.
Then check the thing that is actually blocking it, in this order: the service is bound to0.0.0.0 and not 127.0.0.1 · the host firewall (ufw, firewalld, Windows Defender Firewall) · the cloud security group or the router's port-forward rule · and finally your ISP, which commonly blocks 25, 80 and 445 on residential lines whatever you configure.
What a browser genuinely can verify
One thing: that an HTTPS service answers. If what you actually want to know is “is my site up and how fast is it”, the latency test measures real round trips to a CORS-open URL. If the name doesn't resolve, or resolves somewhere unexpected, that is a DNS problem, not a port problem — and it is the more common cause of “my port is closed” than an actual firewall.
An IP address finds the machine; a port picks which program on it gets the traffic. TCP sets up a connection first — a handshake, ordered delivery, retransmission — which is why the web, email and SSH use it. UDP just sends the packet with no handshake and no guarantee it arrives, which is why DNS, video calls and games use it: late data is worse than lost data.
That difference is why a UDP port is so much harder to test. TCP either completes a handshake or it doesn't, so a tool can tell you. A UDP service that has nothing to say to an unexpected packet stays silent — and silence looks identical to a firewall dropping it.
The three ranges
0–1023Assigned by IANA to core services. On Unix, binding one needs root (or CAP_NET_BIND_SERVICE).1024–49151Registered by vendors for their applications. Any user can bind these — which is why every dev server lives here.49152–65535Never assigned. The OS hands these out as the SOURCE port of your outgoing connections. (Linux actually uses 32768–60999 by default.)Closed is not the same as filtered
Closed means the host answered: the packet arrived, nothing is listening, and you got an immediate refusal (a TCP RST). Filtered means nothing answered at all — a firewall dropped your packet in silence, so you wait for a timeout and learn nothing. The difference matters: closed proves the host is reachable and the port is free; filtered tells you only that something between you and it is discarding traffic.nmap reports the two separately. A browser cannot distinguish them, which is why this page reports a timeout as “can't tell” rather than guessing.
The one habit worth keeping
Bind services to 127.0.0.1 instead of 0.0.0.0 unless something outside the machine genuinely needs them, and reach them over SSH or a VPN. Every database on the never-expose list above ships with that advice, and the leaks all begin the same way: a default bind address, a cloud instance with a public IP, and a scanner that found it within the hour.
The blocked-port list this page uses is the WHATWG Fetch Standard's “bad port” table — the ports every browser refuses to connect to (Chrome calls it ERR_UNSAFE_PORT). Local probing is additionally gated by Chrome's Local Network Access permission, which replaced Private Network Access and ships in Chrome 142.
FAQ
Is it safe to expose Redis on port 6379?
No. Without authentication it is full read and write access, and a writable Redis can usually be escalated to command execution on the host. Bind to 127.0.0.1 or a private network, set a strong password, and use TLS if the traffic crosses anything shared.
Does Redis require a password by default?
Historically no, and that default still shapes a lot of deployed configuration. Protected mode blocks remote clients when nothing is configured, but it disengages as soon as a bind address or password is set, so it is not a substitute for configuring both.
How does an open Redis lead to code execution?
By abusing persistence: an attacker sets the save directory and filename to a location the system reads — a cron directory, or a user’s .ssh/authorized_keys — and writes a payload as the dataset. Renaming or disabling the CONFIG command removes that path.