Install libpam-abl by entering the following commands in the terminal:
sudo apt update sudo apt install libpam-abl
Description:
blocks hosts attempting a brute force attack
a PAM module that provides auto blacklisting of hosts and users responsible for repeated failed authentication attempts. Generally configured so that blacklisted users still see normal login prompts but are guaranteed to fail to authenticate.
Homepage: http://pam-abl.sourceforge.net
Version: 0.6.0-5
Section: universe/admin