In 2012 cybercriminals figured out how to abuse DNS to generate vast DDoS 'reflection' attacks, which can be thought of as a way of creating a lot of traffic for very little input. By 2013, they’d moved on to Network Time Protocol (NTP), Simple Network Management Protocol (SNMP), followed by Simple Service Discovery Protocol (SSDP) not long after.

Spot a pattern here? The DDoS attacks welling up on the back of lazy server misconfigurations running these services were sometimes spectacular, certainly worrying. Admins rushed to fix the vulnerabilities but every time they did the cybercriminals moved on to a new protocol or service and so the pattern repeated itself.


DDoS mitigation firms now regularly warn about any number of common but little considered protocols and so it has come to pass that another obscure service, Portmapper, has now joined the list of the abused.

What has happened? Big network operator Level 3 noticed a newish type of DDoS attack misusing the Portmapper (aka RPCbind) service. It's been happening for a while but has recently ramped dramatically.

When did this spike happen: between late June and mid-August

What is RCS Portmapper? Mainly a legacy Unix directory service that allows a program running somewhere (i.e. on a PC) to make a Remote Procedure Call to a program running somewhere else (i.e. a server). It’s been around for years

What did the attackers do? Sent UDP packets to public Portmapper servers using spoofed addresses pointing at the DDoS target. Portmappper then helpfully replied with a much larger response. If enough servers are queried like this without anyone realising, the attack is ‘amplified’, overwhelming the target.

How easy is it to abuse? It should be something used only by interval LANs and not reachable externally - apparently many servers have been left exposed.

Is it serious? Allowing an external party to reach the Portmapper service is bad. Allowing that server to inadvertently DDoS a third party even worse.

How much traffic did it detect? By comparison with other abused protocols, very little but the firm wants people to address the issue before things get worse – they usually do if ignored.

Is there a fix? There is no specific software flaw – the Portmapper service is working as it was designed to. The solution is to disable or block external access to the service.

Other abused protocols: DNS, NTP, Chargen, Netbios, SNMP, SSDP

Level 3 quote: “We recommend disabling Portmapper along with NFS, NIS and all other RPC services across the open Internet as a primary option. In situations where the services must remain live, firewalling which IP addresses can reach said services and, subsequently, switching to TCP-only are mitigations to avoid becoming an unknowing participant in DDoS attacks in the future.