{
  "port": 255,
  "protocol": "tcp",
  "service": "Unassigned",
  "oneLiner": "Another unassigned port in the 250–255 gap, with no protocol behind the number.",
  "whatItIs": "IANA lists no assignment for 255 on either transport, and there is no historical registration to point at. Like its neighbour 254 it still carries a measurable open-rate in Nmap's frequency data, so it rides along in default scans and turns up in results as a nameless open port. Any listener is site-specific: an internal service someone parked on a low, memorable number, or a device firmware default that was never registered. There is nothing generic to say about what it does.",
  "exposure": {
    "verdict": "careful",
    "note": "Unregistered does not mean harmless — fingerprint the listener before exposing it, because low-numbered ports usually mean a root-owned process."
  },
  "checkCommand": "nmap -sV -p 255 TARGET",
  "links": [
    {
      "title": "IANA Service Name and Transport Protocol Port Number Registry — 255",
      "url": "https://www.iana.org/assignments/service-names-port-numbers/service-names-port-numbers.xhtml?search=255",
      "kind": "iana"
    },
    {
      "title": "nmap-services — the empirical port frequency list (255/tcp \"unknown\")",
      "url": "https://github.com/nmap/nmap/blob/master/nmap-services",
      "kind": "github"
    }
  ]
}