That is: MITM SSH connections to these devices without getting any warning.
Of course you first have to get in a position to MITM the person who connects to these devices.
http://www.gremwell.com/ssh-mitm-public-key-authentication
You'd still be able to impersonate the server, but that's less useful in the general case unless you can emulate the remote machine convincingly long enough to gather useful information.
Even the thing you link to actually says:
> The algorithm itself does not protect against active MITM attack, but it makes it impossible for MITM attacker to influence the choice of the shared key (and by extension the session ID) by the victims.
Does not protect against active MITM attack. It _does_ keep an attacker from influencing choice of shared key, but an active MITM attack is still in the middle and doesn't need to influence choice of shared key to mount many many kinds of attacks.
The attacker just has to authenticate with the correct signature to each, but if it's an attacker, why would it just pass along the victim's data anyway? The whole point of an MITM is that you can modify data before it hits its target.
Thus, all these machines with duplicate keys are VERY vulnerable to MITM, because anyone with access to one of them has access to the private key.
"there are no tools implementing MITM against an SSH connection authenticated using public-key method ... Being pressed to produce a PoC for this attack, I have attempted to implement it only to discover it is quite impossible and here is why."