Dream Machine Pro

[simgate]

Attempting to SSH into Ubiquiti Dream Machine Pro. The device shows as offline, and SSH authentication failed. However, works with PuTTY. Seems to be an issue with it not accepting the key?

[jpstruhar]

I'm having exactly this problem with a UDM Pro. I can SSH in via Terminal or Putty but not omnyssh.
Claude Insights:
That log is very telling — and it points to something different from (and much more concrete than) the algorithm-negotiation theory. Look at this line:

debug1: Authentications that can continue: publickey,keyboard-interactive

The UDM Pro's SSH server does not advertise the "password" auth method at all — only publickey and keyboard-interactive. Your PowerShell session only got in because OpenSSH automatically fell back to keyboard-interactive and sent your password as the answer to that interactive prompt:

debug1: Next authentication method: keyboard-interactive
...
(root@ip) Password:
...
Authenticated to ip ([ip]:22) using "keyboard-interactive".

That's the key detail. This is a common UniFi/UDM quirk — many of their SSH daemons disable the plain SSH password auth method and only allow keyboard-interactive, even though from a user's perspective it still looks and feels like "just typing a password."

Let me check whether that's what's tripping up russh specifically.

That confirms it precisely. This is the root cause:

The UDM Pro's SSH server doesn't offer the password authentication method at all — only publickey and keyboard-interactive. When you type your password in PowerShell or SolarPutty, you're not actually doing SSH "password" auth — the client is silently falling back to keyboard-interactive and submitting your password as the answer to that interactive prompt instead. That's a very deliberate, standard SSH client behavior that's been baked into OpenSSH (and PuTTY-derived tools like SolarPutty) for decades, so it's invisible to you as the user.

OmnySSH's password field in hosts.toml, running over russh, almost certainly calls russh's authenticate_password() — the literal SSH password auth method. Since the UDM Pro's sshd never lists password as an allowed method, that request gets rejected outright, before your actual password is even meaningfully checked. Your credentials are correct; the auth method OmnySSH is using isn't one the server accepts.

Notably, current russh (0.63.1) does support keyboard-interactive as a method — so this isn't a hard library limitation, it's a matter of whether OmnySSH's code actually tries it as a fallback when password gets rejected. Many thin wrappers around russh implement only straight password auth and never wire up the keyboard-interactive path, since it's more code (handling prompts, submethods, etc.) for what looks like the same thing to a user.

What I'd do from here:

This isn't something fixable from your side (UDM Pro's SSH config isn't something you can persistently edit — UniFi OS manages/resets it) — the fix has to be in OmnySSH.
Worth filing a GitHub issue on timhartmann7/omnyssh with exactly what you gave me: the Authentications that can continue: publickey,keyboard-interactive line from your verbose log, and asking whether their SSH engine falls back to keyboard-interactive when password auth is rejected. That's a very actionable, specific bug report.
In the meantime, SolarPutty (or plain ssh) remains your working option for this device.

[tomvanswam]

I also encountered this on my Snapmaker U1. Also no password auth possible.

[timhartmann7]

Thanks for the detailed log, that pinned it down. The UDM Pro only takes a password through keyboard-interactive, and OmnySSH was sending it with the plain password method, so the console turned it down. That's fixed in #112: the saved password now goes through keyboard-interactive too, the same way PuTTY and ssh do it. It'll be in the next release, which is coming soon.

If you actually log in with a key from PuTTY/Pageant rather than a password, let me know. That's a separate case.

[jpstruhar]

I'll wait for the update, thanks so much. I noticed I'd been using a password rather than a key for the UDM Pro in SolarPuTTY, so either a key wasn't possible or it was a pain to set up.

[simgate]

Thanks! You're awesome!

[jpstruhar]

Confirmed fixed and working in 1.1.4