Port 503Intrinsa

Port 503 carries the Intrinsa service over TCP or UDP.

Technical Details

what runs on :503

Intrinsa is registered on port :503 over tcp and udp to Robert Ford. We don't have a technical write-up for it beyond the IANA registry entry.

In nmap's internet-wide scan data this port is found open rarely. What's listening is often not the registered service, so check before you assume.

find what's listening on :503

this machine

# linux
sudo ss -tulpn 'sport = :503'

# macos / bsd
sudo lsof -nP -i :503

# windows (then: tasklist /FI "PID eq <pid>")
netstat -ano | findstr :503

another host

nmap -sV -p T:503 <host>
sudo nmap -sU -sV -p U:503 <host>

run it? the handshake, the implementations you meet in the wild and the flags that matter come from the engineers who do.

exposure of :503

risk score

1/ 10safe

routine exposure. this port is rarely the way in on its own — keep it patched and logged and move on.

in transit

cleartext

credentials and payloads are readable by anyone on path

assignment

official

registered with iana for this service — scanners fingerprint it by number

reachable over

tcp · udp

udp is connectionless — source addresses are trivially spoofed and it is a reflection favourite

security overview

no security notes recorded for :503 yet

known exploits, hardening advice, what a compromise looks like — suggest an edit if you know its exposure.

ports registered around :503, by lookups.

port	service	proto	category	risk	views
:443	HTTPS	TCPtls	Web Services	caution	65.9k
:548	Apple Filing Protocol	TCP	File Transfer	caution	36.8k
:445	Microsoft-DS / SMB	TCP	File Transfer	caution	22.3k
:475	tcpnethaspsrv	TCP	Security	caution	20.7k
:502	Modbus Protocol	TCPUDP	Network Services	caution	19.2k
:563	NNTPS	TCPUDPtls	Web Services	safe	18.1k
:546	DHCPv6 Client	TCPUDP	Network Services	caution	16.6k
:547	DHCPv6 Server	TCPUDP	Network Services	caution	14.5k

risk mix of the 8 listed

2 of 8 encrypted