More than 10 percent of Internet’s DNS (DNS) servers are still vulnerable to cache-poisoning attacks. This is despite it being several months since the vulnerabilities were disclosed and fixes made available. One of the first DNS servers compromised by a cache poisoning attack was one used by the author, HD Moore. The antidote to the vulnerability is port randomization, which makes it harder for an attacker to guess which port to send poisoned data to, but it doesn’t make an attack impossible.”]
Source: https://www.csoonline.com/article/2123396/survey–one-dns-server-in-10–trivially-vulnerable-.html