Hacking Linux Exposed: SSH Bouncing--How to Get Through Firewalls Easily
"The first and most simple solution is to SSH to the machine in the way, say the firewall. The firewall administrator can just set up one or more non-privileged accounts for users who need access to the machines behind it. This is a pain, of course--if you want to upload a file, you need to upload it to the firewall via sftp/scp, and then upload it to the target server. What a pain. And security-wise, you now have all these random firewall accounts running amok, probably not your favourite situation..."
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