Algorithm negotiation fail SSH in Jenkins

Question

I\'m trying to ssh from Jenkins to a local server but the following error is thrown:

[SSH] Exception:Algorithm negotiation fail
    com.jcraft.jsch.JSchExcep         


        

Answer 1

In my case - OpenSSH_6.7p1 on server - I had to modify KexAlgorithms and MACs (additional hmac-md5,hmac-sha1,hmac-sha1-96,hmac-md5-96 values):

KexAlgorithms curve25519-sha256@libssh.org,ecdh-sha2-nistp256,ecdh-sha2-nistp384,ecdh-sha2-nistp521,diffie-hellman-group-exchange-sha256,diffie-hellman-group14-sha1,diffie-hellman-group-exchange-sha1,diffie-hellman-group1-sha1

MACs hmac-sha2-512-etm@openssh.com,hmac-sha2-256-etm@openssh.com,hmac-ripemd160-etm@openssh.com,umac-128-etm@openssh.com,hmac-sha2-512,hmac-sha2-256,hmac-ripemd160,umac-128@openssh.com,hmac-md5,hmac-sha1,hmac-sha1-96,hmac-md5-96

Above should be put placed:

/etc/ssh/sshd_config

And then restart the ssh:

sudo /etc/init.d/ssh restart

Answer 2

Instead of fixing this on the server side, you can also update the client side. If you use http://maven.apache.org/wagon/wagon-providers/wagon-ssh/ in a newer version (>= 2.12 - current release as of Sep. 2018 is 3.2.0), this problem does not occur anymore.

<project>
  <!-- ... -->
  <build>
    <pluginManagement>
      <plugins>
        <plugin>
          <groupId>org.apache.maven.plugins</groupId>
          <artifactId>maven-site-plugin</artifactId>
          <version>3.6</version>
          <dependencies>
            <dependency>
              <groupId>org.apache.maven.wagon</groupId>
              <artifactId>wagon-ssh</artifactId>
              <version>3.2.0</version>
            </dependency>
          </dependencies>
        </plugin>
      </plugins>
    </pluginManagement>
  </build>
  <!-- ... -->
</project>

Update 2018-10-21: The latest version is now 3.2.0. Due to various vulnerability issues I'd advise to always use a current version of SSH- or SSL-related software anyway. So please check and update your dependencies in your code.

Answer 3

I have faced exactly same problem. AS Matthieu suggested we have to add some key-exchange algoritm in sshd-config file present in cygwin>etc>sshd_config. I have just added following and its worked for me,

KexAlgorithms diffie-hellman-group1-sha1,curve25519-sha256@libssh.org,ecdh-sha2-nistp256,ecdh-sha2-nistp384,ecdh-sha2-nistp521,diffie-hellman-group-exchange-sha256,diffie-hellman-group14-sha1

But the file itself is in read only mode so we have to provide it all access like read,write and execute though comand prompt. "chmode 777 sshd_config". then add above mention algorithms. stop the sshd service through "net stop sshd" and then start it "net start sshd".

Have fun....

Answer 4

We had the same problem with our jenkins (2.21) and the SSH plugin (2.4)

Our solution is to use the nativ shell execution. It seems that the jenkins plugins does not use the same ssh connection settings than the nativ shell.

So you could make the ssh connect like this (without the ssh-plugin):

ssh user@host <<'ENDSSH'
 echo your remote command here
ENDSSH 

If you wrap your remote commands with the code above the connection works fine.

With this solution you dont need the ssh-plugin anymore.

For your information: We got the problem on our mittwald servers since they upgraded the openssh on there servers.

Answer 5

TL;DR edit your sshd_config and enable support for diffie-hellman-group-exchange-sha1 and diffie-hellman-group1-sha1 in KexAlgorithms:

KexAlgorithms curve25519-sha256@libssh.org,ecdh-sha2-nistp256,ecdh-sha2-nistp384,ecdh-sha2-nistp521,diffie-hellman-group-exchange-sha256,diffie-hellman-group14-sha1,diffie-hellman-group-exchange-sha1,diffie-hellman-group1-sha1

I suspect that the problem appeared after the following change in OpenSSH 6.7: "The default set of ciphers and MACs has been altered to remove unsafe algorithms.". (see changelog). This version was released on Oct, 6, and made it on Oct, 21 to Debian testing (see Debian changelog).

OpenSSH enables only the following key exchange algorithms by default:

• curve25519-sha256@libssh.org
• ecdh-sha2-nistp256
• ecdh-sha2-nistp384
• ecdh-sha2-nistp521
• diffie-hellman-group-exchange-sha256
• diffie-hellman-group14-sha1

Whereas JSch claims to support these algorithms (see under "features") for key exchange:

• diffie-hellman-group-exchange-sha1
• diffie-hellman-group1-sha1

So indeed, they cannot agree on a common key exchange algorithm. Updating sshd_config (and restarting the SSH server) does the trick. Apparently JSch is supposed to support the "diffie-hellman-group-exchange-sha256" method since version 0.1.50 (see changelog).

Answer 6

I also faced same problem with similar exceptions on Jenkins console. Then I tried Matthieu Wipliez's solution. But it did not work as same configuration was already done on my SSH server(Remote machine: Linux ubuntu 16.04).

After spending few hours, I just checked my SSH plugin's version which was 2.1 and I just updated it to latest (2.5).

And guess what it worked!!

I do not know whether it will work in every similar case but I would like to suggest try it first. It may save your time.