{
  "port": 21571,
  "protocol": "tcp",
  "service": "Unassigned",
  "oneLiner": "Unassigned by IANA with no documented service — present in default scans on frequency alone.",
  "whatItIs": "21571 falls in IANA's unassigned range 21555-21589 and has no registration. Nmap's table names it 'unknown' with a small but nonzero open-frequency, which is the only reason it appears in the default top-1000 TCP scan. Nothing in the public record ties it to a product, protocol, or malware family. Whatever you find open here was put there by someone locally.",
  "exposure": {
    "verdict": "careful",
    "note": "No standard service means no default guidance. Identify the listener and inherit that service's exposure rules."
  },
  "checkCommand": "nc -vz TARGET 21571",
  "links": [
    {
      "title": "IANA Service Name and Transport Protocol Port Number Registry",
      "url": "https://www.iana.org/assignments/service-names-port-numbers/service-names-port-numbers.xhtml",
      "kind": "iana"
    },
    {
      "title": "Nmap nmap-services frequency table",
      "url": "https://github.com/nmap/nmap/blob/master/nmap-services",
      "kind": "github"
    }
  ]
}