Net::LibSSH versions before 0.004 for Perl authenticate to an unverified server because connect never checks the host key against known_hosts. connect reports success as soon as ssh_connect returns SSH_OK. libssh leaves the known-hosts check to the application, and this binding never makes it, so the strict_hostkeycheck and knownhosts options are set on the session and then decide nothing. Password, agent and public-key authentication, channel and SFTP operations all run on a session whose peer was never identified, so an attacker who can redirect the connection receives the password when password authentication is used, and commands and data sent over the session.