Unassigned, unnamed, and one of the more frequently-open unregistered ports in Nmap's data.
IANA lists 23502 in the unassigned range 23458-23545. Nmap labels it 'unknown' but gives it a relatively high open-frequency for an unregistered port, so scans find something answering on a noticeable share of hosts without any identification. No public documentation associates it with a product or protocol. As with the rest of this block, the port number tells you nothing; the banner does.
Expose with care
A commonly-open but unidentified port is worth investigating on your own hosts before it is worth exposing on anyone's.
$ nmap -Pn -sV -p 23502 --reason TARGETSeen 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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Corrections or a missing port? Reply @rimrocksystems.