openssh unix dev - Feb 2019 - Possible bug: SSH doesn't prefer host keys listed in SSHFP records while connecting.

The reason why this is a bug is, for example, that if the server was
updated and it re-generated the ECDSA key you deleted, you would have
to do some non-obvious steps for your client to ignore it.

On Sat, Feb 23, 2019 at 11:49 AM Damien Miller <djm at mindrot.org>
wrote:
>
> On Fri, 22 Feb 2019, Yegor Ievlev wrote:
>
> > Steps to reproduce:
> > 1. Run a SSH server with default configuration and point a domain to
it.
> > 2. Add SSHFP record to the domain, but only for Ed25519 key.
> > 3. Attempt to connect with VerifyHostKeyDNS set to yes, but the rest
> > of settings set to defaults.
> > 4. OpenSSH defaults to ECDSA instead of Ed25519 and refuses connection
> > because there is no ECDSA fingerprint in SSHFP records.
>
> I'm not seeing the bug: typically you'd add SSHFP records for all
> the server's hostkeys, but you've not done this.
>
> -d

On Sat, 23 Feb 2019, Yegor Ievlev wrote:
> The reason why this is a bug is, for example, that if the server was
> updated and it re-generated the ECDSA key you deleted, you would have
> to do some non-obvious steps for your client to ignore it.
No, that would also be a misconfiguration. If your SSHFP keys don't
match your hostkeys then you're doing it wrong.

-d

Ok, thanks for the clarification.

On Sun, Feb 24, 2019 at 2:23 AM Damien Miller <djm at mindrot.org>
wrote:
>
> On Sat, 23 Feb 2019, Yegor Ievlev wrote:
>
> > The reason why this is a bug is, for example, that if the server was
> > updated and it re-generated the ECDSA key you deleted, you would have
> > to do some non-obvious steps for your client to ignore it.
>
> No, that would also be a misconfiguration. If your SSHFP keys don't
> match your hostkeys then you're doing it wrong.
>
> -d