In certain closed-source implementations.
>"The researchers traced the keys they compromised to devices that used custom, closed-source SSH implementations that didn’t implement the countermeasures found in OpenSSH and other widely used open source code libraries. The devices came from four manufacturers: Cisco, Zyxel, Hillstone Networks, and Mocana. Both Cisco and Zyxel responded to the researchers’ notification of the test results before the completion of the study. Hillstone responded afterward."
