{
  "port": 1503,
  "protocol": "tcp",
  "service": "T.120 data conferencing (imtc-mcs)",
  "oneLiner": "T.120 conferencing — in practice Microsoft NetMeeting's application sharing, whiteboard, chat, and file transfer.",
  "whatItIs": "ITU-T T.123 specifies TCP 1503 as the transport port for the T.120 multipoint data conferencing stack, and IANA registers it as \"imtc-mcs\" to Databeam, one of T.120's authors. The only implementation most people ever met is Microsoft NetMeeting, which used 1503 for program sharing, whiteboard, chat, and file transfer while H.323 audio/video signalling ran on 1720. Microsoft carried the same stack into Windows Live Messenger's sharing features, and both products are long dead. A listener on 1503 today means legacy conferencing software on an old Windows box.",
  "exposure": {
    "verdict": "never",
    "note": "T.120 program sharing hands a remote party control of the desktop, with authentication that is per-conference at best — this belongs on no internet-facing host, and the software behind it has been unpatched for over a decade."
  },
  "checkCommand": "nmap -sV -p 1503 TARGET",
  "links": [
    {
      "title": "ITU-T Recommendation T.123 — Network-specific data protocol stacks for multimedia conferencing",
      "url": "https://www.itu.int/rec/T-REC-T.123",
      "kind": "spec"
    },
    {
      "title": "[MS-SDP]: Application Sharing and Whiteboarding",
      "url": "https://learn.microsoft.com/en-us/openspecs/windows_protocols/ms-sdp/b4c65407-d899-4096-b150-d4eb856cac25",
      "kind": "official-docs"
    },
    {
      "title": "IANA port registry — 1503",
      "url": "https://www.iana.org/assignments/service-names-port-numbers/service-names-port-numbers.xhtml?search=1503",
      "kind": "iana"
    }
  ]
}