The company's alert warns owners of devices that ship with Plex Media Server, a web application for Windows, Mac, and Linux that's usually used for video or audio streaming and multimedia asset management.
Netscout says that when a server/device running a Plex Media Server app is booted and connected to a network, it will start a local scan for other compatible devices via the Simple Service Discovery Protocol (SSDP).
The problem comes when a Plex Media Server discovers a local router that has SSDP support enabled. When this happens, the Plex Media Server will add a NAT forwarding rule to the router, exposing its Plex Media SSDP (PMSSDP) service directly on the internet on UDP port 32414.
Since the SSDP protocol has been known for years to be a perfect vector to amplify the size of a DDoS attack, this makes Plex Media servers a juicy and untapped source of DDoS bots for DDoS-for-hire operations.
Netscout says that attackers only have to scan the internet for devices with this port enabled, and then abuse them to amplify web traffic they send to a DDoS attack victim.
According to Netscout, the amplification factor is around 4.68, with a Plex Media server amplifying incoming PMSSDP packets from 52 bytes to around 281 bytes, before sending the packet to the victim.
27K+ Plex Media servers are exposed on the internet
The security firm said it scanned the internet and found 27,000 Plex Media servers left exposed online that could be abused for DDoS attacks.
Furthermore, some servers have already been abused. Netscout said that not only did it saw DDoS attacks using Plex Media servers, but that this vector is now becoming common.
"As is routinely the case with newer DDoS attack vectors, it appears that after an initial period of employment by advanced attackers with access to bespoke DDoS attack infrastructure, PMSSDP has been weaponized and added to the arsenals of so-called booter/stresser DDoS-for-hire services, placing it within the reach of the general attacker population," the company said.
According to Netscout, past PMSSDP attacks have reached around 2-3 Gbps, but the servers could be combined with other vectors for much larger attacks.
This is Netscout's second warning about a new DDoS attack vector being discovered abused in the wild this year. In January, the company warned that Windows Remote Desktop Protocol (RDP) servers were also being abused for DDoS attacks.
A Plex spokesperson told ZDNet today that the company is currently working on a patch that "adds an extra layer of protection for those servers that may have been accidentally exposed," which the company plans to release soon.