{
  "port": 9100,
  "protocol": "tcp",
  "service": "Raw printing (AppSocket / JetDirect, PDL data stream)",
  "oneLiner": "A network printer: send bytes, they print — no protocol, no login.",
  "whatItIs": "Registered with IANA as pdl-datastream / hp-pdl-datastr, this is the AppSocket protocol, better known as JetDirect after the HP print servers that popularised it. There is no handshake and no authentication: the client opens the socket, writes a page description stream such as PostScript, PCL, or ZPL, and closes it. CUPS drives it with the socket backend (socket://host:9100), and it is one of the most commonly open ports on any office network. Label printers, MFPs, and print server appliances all sit here.",
  "exposure": {
    "verdict": "never",
    "note": "Anyone who can reach the port can print, waste consumables, and on many devices push firmware or PJL commands that change settings — there is no authentication in the protocol at all."
  },
  "checkCommand": "nc -vz -w 3 TARGET 9100",
  "links": [
    {
      "title": "CUPS — Network printing (AppSocket/JetDirect on port 9100)",
      "url": "https://www.cups.org/doc/network.html",
      "kind": "official-docs"
    },
    {
      "title": "IANA port registry — 9100 (pdl-datastream)",
      "url": "https://www.iana.org/assignments/service-names-port-numbers/service-names-port-numbers.xhtml?search=9100",
      "kind": "iana"
    }
  ]
}