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PuTTY Private Keys 
 


Added: 01/19/2007, Hits: 3,109, Rating: 0, Comments: 0, Votes: 0
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We recently discovered that our server had been hacked and turned into a zombie joining the ranks of millions of other servers worldwide. We discovered this while investigating the cause of frequent server crashes. It turns out, the hackers were using our server to send out a constant stream of spam using Sendmail from our server which was eating up all of the resources and crashing it. I discovered this after noticing that the /var/spool/mqueue folder was loaded with outgoing messages.

While finding the original entry point and patching any applications with security holes is very important, there is something else you should do to prevent anything like this from happening to you. The hackers opened a back door and gave themselves access to SSH. Once they have root command-line access, they can do just about anything so it is very important to lock down access to SSH. An easy way to do this is to set up PuTTY Private Keys. A private key is a file that you generate using PuTTYgen and save to your local hard drive.

You then configure the server to only allow access to SSH if the user has this .ppk file which can also be password protected to add an additional layer of security. Password protecting the .ppk file prevents unauthorized access even if your client computer is compromized. The end result is that ONLY a person with this .ppk file and the associated password can access your server via SSH.

There is a very good tutorial on setting this up here.





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