Unregistered, but common enough in Nmap's corpus to make every default scan.
64623 carries no IANA registration, per RFC 6335's rule that the Dynamic/Private range is never assigned. Nmap's nmap-services rates it "unknown" at 0.000760 — high for an unnamed port in this band, on par with 52869 and 55555 — which guarantees its place in the default top-1000 TCP list. Despite that frequency, SANS ISC still shows no service name and no tracked vulnerabilities. Something binds this port often enough to register statistically, and no public source says what.
Expose with care
Frequently observed and never identified is not a reassuring combination. Find the process locally rather than assuming it is benign.
$ sudo lsof -nP -iTCP:64623 -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.