The article explains the novelty as: “[T]he researchers found a very clever trick: they leverage ICMP rate limits as a side channel to reveal whether a given port is open or not. ICMP rate limiting was introduced (somewhat ironically, given this attack) as a security feature to prevent a server from being used as an unwitting participant in a reflection attack.“ The suggested mitigation is Linux kernel upgrade to roll out unpredictable ICPM rate limiting.