nvOC through 3.2 ships with SSH host keys baked into the installation image, which allows man-in-the-middle attacks and makes identification of all public IPv4 nodes trivial with Shodan.io. NOTE: as of 2019-12-01, the vendor indicated plans to fix this in the next image build.
https://github.com/papampi/nvOC_by_fullzero_Community_Release/commits/release