ProxyJump is safer than SSH agent forwarding

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2021-06-12 16:00:07

By Virag Mody , InfoWorld |

An SSH jump server is a proxy standing between clients and the rest of the SSH fleet. Jump hosts minimize threats by forcing all SSH traffic to go through a single hardened location and minimizing an individual node’s SSH endpoints to the outside world. (Read more: “How to set up an SSH jump server.”)

One way to configure a multi-hop setup is by storing a private key for the destination server on your jump server. Do not do this. A jump server is usually a multi-user environment, meaning any single party with elevated privileges could compromise any private key. A solution to this security threat is enabling agent forwarding. Given how common this method is, it may surprise you to learn this is not recommended. To understand why, let’s dig a bit deeper.

ssh-agent is a key manager that exists as a separate program from SSH. (Read more: “How to manage SSH keys.”) It holds private keys and certificates used for authentication in memory. It does not write to disk or export keys. Instead, the agent’s forwarding feature allows our local agent to reach through an existing SSH connection and authenticate on a remote server through an environment variable.