PostgreSQL client protocol, TCP 5432.
The postgres server listens on TCP 5432 by default (the port parameter), and listen_addresses defaults to localhost, so an out-of-the-box install accepts only loopback TCP plus Unix-domain sockets. Seeing it on a scan means someone set listen_addresses to '*' or a real interface — common for containerized deploys, managed database endpoints, and pgbouncer front-ends. Who may connect from where is then decided by pg_hba.conf, which is a separate gate from the listener.
Do not expose
Keep it on localhost or a private network; if it must cross a network, require hostssl plus scram-sha-256 in pg_hba.conf rather than relying on the port being obscure.
$ psql -h DB_HOST -p 5432 -U postgres -c 'SELECT version();'Seen this on your network? Beige Box scans your Wi-Fi and shows every open port on every device — and its Ports tool links straight back here.
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