Port reference
Port 623 (UDP) – IPMI / RMCP
IPMI over RMCP — out-of-band management of server baseboard management controllers (BMC).
Quick facts
- Transport
- udp
- Category
- Registered
- Risk level
- Critical
Actively exploited and high-impact — keep it off the public internet.
Default state
Open on server BMCs (iDRAC, iLO, IMM, BMC) for remote power, console, and firmware control, often on a poorly segmented management network.
What is port 623 used for?
Port 623 carries IPMI over RMCP, the protocol used to manage a server's baseboard management controller (BMC). The BMC is a small dedicated chip on server hardware — Dell iDRAC, HPE iLO, and Supermicro IPMI are common examples — that lets administrators power the machine on or off, view the console, mount virtual media, and check hardware health remotely, even when the main operating system is down. This is known as out-of-band management.
When would you open it?
You open port 623 only if you operate physical servers and need remote management of their BMCs, typically inside a datacenter. It belongs on a dedicated management network reachable by your administrators, never on a public-facing interface.
Is it safe to open?
IPMI has well-known weaknesses and gives total control of the hardware, so never expose it to the internet; keep it on an isolated management network reached over a VPN. See the security notes below.
How to check if this port is open
ss -tulpn | grep :623
nmap -sU -p 623 <target>netstat -ano | findstr :623
Test-NetConnection <host> -Port 623 # TCP onlylsof -i :623
nmap -sU -p 623 <target>How to open this port on your router
To reach this service from outside your network, forward the port on your router:
- Open your router's admin page (usually http://192.168.1.1 or http://192.168.0.1) and sign in.
- Find the "Port Forwarding" section — it may be called NAT, Virtual Server, or Applications & Gaming.
- Add a rule forwarding external port 623 to your device's local IP, internal port 623, protocol UDP.
- Save and reboot the router if prompted, then test the port from outside your network.
Only forward ports you understand — it exposes that device to the public internet. For remote admin access, a VPN is safer than forwarding the port.
Allow this port through the firewall
sudo ufw allow 623/udpsudo firewall-cmd --permanent --add-port=623/udp
sudo firewall-cmd --reloadsudo iptables -A INPUT -p udp --dport 623 -j ACCEPTNew-NetFirewallRule -DisplayName "Allow 623" -Direction Inbound -Protocol UDP -LocalPort 623 -Action AllowSecurity & risks
Common attacks
- RAKP password-hash retrieval for offline cracking (CVE-2013-4786)
- Cipher-zero authentication bypass (no password required)
- Default and weak BMC credentials
- Full server takeover: power, virtual media, console
Hardening
- Isolate BMCs on a dedicated, firewalled management VLAN
- Never expose UDP 623 to the internet
- Disable cipher suite 0 and anonymous logins
- Change default credentials; use long unique passwords
- Keep BMC firmware patched; restrict by IP allowlist
How to block this port
sudo ufw deny 623/udpsudo firewall-cmd --permanent --remove-port=623/udp
sudo firewall-cmd --reloadsudo iptables -A INPUT -p udp --dport 623 -j DROPNew-NetFirewallRule -DisplayName "Block 623" -Direction Inbound -Protocol UDP -LocalPort 623 -Action Blocknmap snippet
nmap -sU -p623 --script ipmi-version,ipmi-cipher-zero,ipmi-brute <target>Replace <target> with the host or range you're authorized to scan.
Related ports
Frequently asked questions
- Why is IPMI on port 623 so dangerous?
- The BMC sits below the OS with full hardware control. A compromised IPMI service lets an attacker power-cycle, mount virtual media, and access the console — owning the server regardless of OS hardening.
- What is the IPMI cipher-zero flaw?
- Cipher suite 0 disables authentication on the IPMI 2.0 session, so anyone reaching port 623 can issue privileged commands without a valid password. It must be disabled.