The Simple Service Discovery Protocol (SSDP) is a network protocol based on the Internet Protocol Suite for advertisement and discovery of network services and presence information. It accomplishes this without assistance of server-based configuration mechanisms, such as the Dynamic Host Configuration Protocol (DHCP) or the Domain Name System (DNS), and without special static configuration of a network host. SSDP is the basis of the discovery protocol of Universal Plug and Play (UPnP) and is intended for use in residential or small office environments.
Running an open (UDP) service is not bad on its own and it is mostly a required dependancy when installing a system. Unfortunately, hackers have also found this feature useful in performing a special type of DDoS attack called a 'Amplification Attack'.
The attacker sends a packet apparently from the intended victim to some server on the Internet that will reply immediately. Because the source IP address is forged, the remote Internet server replies and sends data to the victim.
That has two effects: the actual source of the attack is hidden and is very hard to trace, and, if many Internet servers are used, an attack can consist of an overwhelming number of packets hitting a victim from all over the world.
But what makes reflection attacks really powerful is when they are also amplified: when a small forged packet elicits a large reply from the server (or servers). In that case, an attacker can send a small packet "from" a forged source IP address and have the server (or servers) send large replies to the victim.
Amplification attacks like that result in an attacker turning a small amount of bandwidth coming from a small number of machines into a massive traffic load hitting a victim from around the Internet.
There is no reason to have this CHARGEN service enabled on a public facing interface. You should either stop te service or make sure it is not reachable from the internet by using RFC1918 spaces or a firewall.