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Although using public key authentication instead of passwords is a great method for increasing the security of SSH transfers, transferring SSH identity keys can be a royal pain. First, you create your key pairs; then, you copy the public key into the correct locations on all the machines you want to log into. The keys must be in a particular format, and you must go into the correct directory with the correct permissions. Fortunately, ssh-copy-id, a slick utility included with OpenSSH, makes it easy.
Continue reading ‘Ssh-copy-id and other ssh tips’ »

pam_abl 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.

Brute force password discovery attacks involve repeated attempts to authenticate against a service using a dictionary of common passwords. While it is desirable to enforce strong passwords for users this is not always possible and in cases where a weak password has been used brute force attacks can be effective.

The pam_abl module monitors failed authentication attempts and automatically blacklists those hosts (and accounts) that are responsible for large numbers of failed attempts. Once a host is blacklisted it is guaranteed to fail authentication even if the correct credentials are provided.

Blacklisting is triggered when the number of failed authentication attempts in a particular period of time exceeds a predefined limit. Hosts which stop attempting to authenticate will, after a period of time, be un-blacklisted.

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