OpenSSH usually comes with a default configuration which provides high compatibility. So even old clients can still connect. However, this compatibility comes at a price because some of the ciphers / algorithms used may be open to vulnerabilities. If you want to strengthen the encryption and get an overview about known vulnarabilities with your OpenSSH Server or Client configuration, ssh-audit is for you.
Continue reading Hardening your OpenSSH Configuration – Do you know about the tool ssh-audit? [updated]