From the VUSec site:
NetCAT shows that network-based cache side-channel attacks are a realistic threat. Cache attacks have been traditionally used to leak sensitive data on a local setting (e.g., from an attacker-controlled virtual machine to a victim virtual machine that share the CPU cache on a cloud platform). With NetCAT, we show this threat extends to untrusted clients over the network, which can now leak sensitive data such as keystrokes in a SSH session from remote servers with no local access. The root cause of the vulnerability is a recent Intel feature called DDIO, which grants network devices and other peripherals access to the CPU cache. Originally, intended as a performance optimization in fast networks, we show DDIO has severe security implications, exposing servers in local untrusted networks to remote side-channel attacks.
Intel agrees this is a significant vulnerability, having awarded NetCAT a bounty and recommending users to “limit direct access from untrusted networks when DDIO & RDMA are enabled“. This essentially means that in untrusted network environments DDIO and/or RDMA should be disabled to provide security. To the best of our knowledge, this is the first time a major hardware vendor like Intel cautions against using a CPU feature in untrusted local networks.