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I am accustomed to using Putty on a Windows box or an OSX command line terminal to SSH into a Western Digital MyCloud NAS, without any configuration of the client.

Ubuntu 16.04 attempts to SSH into the NAS (via LAN):

ssh root@192.168.8.109

Unable to negotiate with 192.168.8.109 port 22: no matching host key type found. Their offer: ssh-dss

This article indicates that the server and client must agree on 4 decisions. As I understand it: the key exchange (kex) algorithm on the NAS side should be upgraded to a secure \ robust kex, which Ubuntu will accept.

Questions:

  1. What decision-making process is to be used to choose a robust kex?
  2. Is there a good kex upgrade procedure for the WD Mycloud?

If you have successfully performed this upgrade on a WD MyCloud please state this in your response. Thank you

2

There is same question on SO. In short, new OpenSSH deprecated DSA keys, because they can't be larger thatn 1024 b. To workaround it, create local configuration file ~/.ssh/config with

Host 192.168.8.109
  HostkeyAlgorithms +ssh-dss

And then you should be able to connect to your host. Do not allow this generally, because the security of these keys is questionable. Other possibility is to use inline way during connection:

 ssh -oHostKeyAlgorithms=+ssh-dss root@192.168.8.109
  • Is it necessary to upgrade openSSH to upgrade the key exchange? – gatorback Oct 14 '16 at 15:17
  • The best would be to update the SSH on the NAS. But if it is LAN, it does not matter much and you can use the above workaround. – Jakuje Oct 14 '16 at 15:20
  • Yes, I agree. I see this as a learning opportunity close up a security vulnerability on the NAS side. It is important to me to upgrade correctly the first time and not bork-up the NAS: any references \ suggestions are appreciated. Thank you – gatorback Oct 14 '16 at 15:41
  • I would not say, it is security vulnerability. It is just something not-future proof, but if you are using it on LAN it really does not matter. If you go outside to the Internet, using a lot of effort, somebody might be able to attack it, but there is really no known and feasible way of doing that. – Jakuje Oct 15 '16 at 8:05

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