The connection was closed by the server: FlowSshTransport: no mutually supported host key algorithm.

[ibrahimsen]

After upgrading SSH.NET to the latest version (2025.0.0), I am encountering the following error when attempting to connect. How can I resolve this issue?

The connection was closed by the server: FlowSshTransport: no mutually supported host key algorithm. Local list: DSA. Remote list: ssh-ed25519-cert-v01@openssh.com,ecdsa-sha2-nistp256-cert-v01@openssh.com,ecdsa-sha2-nistp384-cert-v01@openssh.com,ecdsa-sha2-nistp521-cert-v01@openssh.com,rsa-sha2-512-cert-v01@openssh.com,rsa-sha2-256-cert-v01@openssh.com,ssh-rsa-cert-v01@openssh.com,ssh-dss-cert-v01@openssh.com,Ed25519,ECDSA/nistp256,ECDSA/nistp384,ECDSA/nistp521,RSA/sha2-512,RSA/sha2-256,RSA/sha1. (KeyExchangeFailed).

[Rob-Hague]

Hi, the library has dropped support for DSA because it is very old and we can no longer easily test it (#1558)

The resolution is for the server to use a new host key with a modern algorithm (e.g. Ed25519), or to stay on 2024.2.0

[ibrahimsen]

I understand, but since we use it to connect to customer SFTP servers, we do not manage them. I cannot force the companies regarding this issue. I would like to benefit from the new version features, but this is an obstacle for me. Is it possible to make this configurable?

[Rob-Hague]

I understand the annoyance, I also had one server which only had a DSA host key and I have asked them to upgrade it. But I'm (personally) not interested in bringing it back:

• we can't easily test it
• it's really old, and the small amount of effort that goes into maintaining this library is better spent elsewhere

if you are not satisfied with staying on 2024.2.0 then you can clone the repo and revert 60f3cd8, it applies+builds cleanly on 2025.0.0