ssh on linux harden server

Question

Here I am dealing with a linux harden server. The problem I am facing is that when I try to connect via ssh, an error message pops out.

kex error : did not find one of algos diffie-hellman-group1-sha1 in list diffie-hellman-group-exchange-sha256,diffie-hellman-group14-sha1,diffie-hellman-group-exchange-sha1 for kex algos

On the Internet many suggested to make changes in the config file, but I am not flexible to do that. is there any thing else that can be done on the software side or server side ?

Answer 1

1. Update your client software version to support reasonable kex suite. It does not look like openssh, isn't it?

2. The diffie-hellman-group1-sha1 is potentially vulnerable to Logjam attack and you should not use that.

3. If you really need to, update server config /etc/ssh/sshd_config and add

   KexAlgorithms +diffie-hellman-group1-sha1
   

   (for openssh-7.0+) or

   KexAlgorithms diffie-hellman-group-exchange-sha256,diffie-hellman-group14-sha1,diffie-hellman-group-exchange-sha1 for kex,diffie-hellman-group1-sha1
   

   (for older versions)