Registered to IANA as CGMS, with nothing public describing it.
IANA lists 3003 for TCP and UDP as cgms, "CGMS", with an individual assignee and no reference document. No specification, vendor page, or open implementation is publicly identifiable, and the port is rare in scan data. In practice a listener on 3003 is an application that took a free port near 3000, not the registered service.
Expose with care
Identify the actual process before deciding anything — the registration tells you nothing about what is listening.
$ sudo lsof -nP -iTCP:3003 -sTCP:LISTENSeen 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.