SSDP
SSDP (Simple Service Discovery Protocol) is the discovery mechanism behind UPnP: devices multicast short UDP messages on port 1900 to announce themselves or to ask "who else is here" for things like media servers, smart TVs, printers, and routers on a local network. It is meant to stay inside the local network, since its whole purpose is letting devices find each other without any manual configuration. The security problem appears when a router or device answers SSDP queries from outside the local network as well: because SSDP replies can be considerably larger than the request that triggered them, an internet-reachable SSDP responder can be abused as a UDP amplification source in distributed denial-of-service attacks, and large waves of such abuse involving consumer routers have been documented publicly. Devices should only ever process SSDP traffic from their own local network segment, never from the public internet.
By AdminKit team, Netbase JSC · Updated