OpenSSL version mismatch. Built against 1000105f, you have 10001080

Try apt-get install openssh-server openssh-client.

I had the same issue when I updated my system to Debian Testing. Even though SSH was already installed, in my case it wasn't pulled in for updating when I ran apt-get update && apt-get upgrade and so the system still had the same SSH binaries with the now-outdated libraries linked against it, hence the version mismatch.

I hit this error the following error in my Ubuntu.

OpenSSL version mismatch. Built against 100020bf, you have 1000106f

Here are what I did to fix the issue.

1. Check where is ssh

   \#which ssh
   
   /usr/local/bin/ssh
   

2. Remove the current ssh package.

   sudo apt-get remove openssh-server openssh-client
   

3. Remove ssh file under /usr/local/bin/ssh

4. Reinstall ssh package as follows.

   sudo apt-get install openssh-server openssh-client
   

5. Log out the current session and re-login again. SSH command is back to work and is under /usr/bin/ssh.

   \#which ssh
   
   /usr/bin/ssh
   

Make sure your other SSL packages have the same version number that your openssl package does. Things like libssl1.0.0 and libssl-dev may have a higher or lower version if you've used non-standard repos like debian-testing.

So if your openssl version is, for example, 1.0.1e-2+deb7u11, fixing this is as simple as

apt-get install libssl1.0.0=1.0.1e-2+deb7u11