Neat idea, but I think there&#x27;s a confused deputy(?) attack possible here.<p>Specifically, I think there&#x27;s a missing binding between the SSH session used for authentication and a user&#x27;s web session.<p>Let&#x27;s say that Alice has an account on bob.com.  Mallory sets up mallory.net and sets up demo-ssh.mallory.net as a DNS alias (or TCP proxy) pointing to demo-ssh.bob.com.<p>1. Alice visits mallory.net, which Mallory controls<p>2. Mallory visits bob.com and starts an authentication session.<p>3. bob.com presents an SSH challenge to Mallory<p><pre><code>    ssh demo-ssh.bob.com -l 7d7662f63f70de7714 -p 2222
</code></pre>
4. Mallory forwards the challenge from bob.com to Alice, optionally substituting their own hostname:<p><pre><code>    ssh demo-ssh.mallory.net -l 7d7662f63f70de7714 -p 2222
</code></pre>
5. Alice runs the command to authenticate to &quot;demo-ssh.mallory.net&quot;.  But this actually authenticates Mallory as Alice to bob.com!<p>6. Upon detecting a successful login, mallory.net accepts Alice&#x27;s login to avoid raising suspicion.<p>The only sure sign that this has happened would be that demo-ssh.bob.com and demo-ssh.mallory.net would have the same host keys, but OpenSSH isn&#x27;t designed to prohibit duplicate host keys.