How to find out if my server is compromised?

Question

I have a linux VPS and I received a complaint that my server was scanning on port 22 some other network. How do I find out if it was compromised or not?

score 1 · Answer 1 · edited Apr 13 '17 at 12:14

I answered a question earlier today that has recommendations in this area:

Linux backdoors I should be wary of

If you suspect that it may have been one of your users and your default shell is bash, you can grep through the .bash_history. For example:

grep nmap /home/*/.bash_history

It's notable that your users can modify the history unless you've introduced methods to make it more difficult.

score 0 · Answer 2 · answered Mar 09 '10 at 21:19

0

Well, if you WERE scanning.... what is the doubt?

answered Mar 09 '10 at 21:19

TomTom

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I'm not scanning dude. That is the problem lol – Mar 09 '10 at 22:15
How you know? Take a measurement from outside (firewall, router in front, wahtever). – TomTom Mar 10 '10 at 06:13

score 0 · Answer 3 · answered Mar 09 '10 at 22:32

You have to think outside the box. As in, you can't really trust what's inside the box.

For instance, get your provider to monitor outgoing traffic. Traffic you can't explain => assume the server has been compromised.

Get an image of the hard drive (extracted using trusted binaries) and run forensics.

How to find out if my server is compromised?

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