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Getting EventID 4625 logon failures

The last two days one of our Citrix servers has been getting 4625 logon failures.   They are happening 3 times every minute.  The logon names are all random.  Mohamed, Betty, Sally, etc.

We have a 2nd Citrix server and it is not getting these.   The server that is, is a Hyper-V VM.  

How do I stop these?

audit failure
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J.R. Sitman
Asked:
J.R. Sitman
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3 Solutions
 
Dr. KlahnPrincipal Software EngineerCommented:
To locate the attacker, download a copy of Microsoft TCPView and run it on the system being attacked.  Since the victim is being attacked every 20 seconds, after a few minutes it should be obvious where the attack is coming from.

If it is coming from within your LAN, locate the system currently on the attacking IP address, unplug it from the network and restore it from a clean backup.

If it is coming from outside your LAN, block the offending IP block (at least to the /24 level) at the firewall.

TCP View
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J.R. SitmanAuthor Commented:
I have it running, but don't know what I'm looking for?

tcpview
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Fred MarshallCommented:
Select one of the items / highlighting it.
Then right click and select WhoIs.
Read the result.

I would practice doing this as there's lots of information and reading a number of results should help you understand what you're seeing.
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J.R. SitmanAuthor Commented:
thanks
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J.R. SitmanAuthor Commented:
I clicked on several and most of them state this.

whois
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Fred MarshallCommented:
Can you highlight a few of those so one might see which ones do this?  It sounds like a local host but...
Not exactly to the point but this may be of some help:
http://www.watchingthenet.com/how-to-identify-unknown-network-connections-in-windows.html
Here's another:
http://www.abuseat.org/advanced.html
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Dr. KlahnPrincipal Software EngineerCommented:
Going back to the image you posted originally, there is no information in the source network address field.

Are you sure that the system is being attacked over the network?  It might have been infected and the infection may be using an internal connection to attack.
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J.R. SitmanAuthor Commented:
no I'm not sure. I ran a virus scan this morning and nothing was found
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Fred MarshallCommented:
I would also run Malwarebytes as a good and additional starting point...
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J.R. SitmanAuthor Commented:
doing that already.  Thanks
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J.R. SitmanAuthor Commented:
no solution found as of this post.   Still getting 4625 audit failures every 20 seconds.
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Dr. KlahnPrincipal Software EngineerCommented:
You may need to try this after hours.

Unplug it from the network, let it sit for five minutes, and plug it back in.  See if the attacks stopped for that period.  If they did, the attack is probably external.  If they did not, the attack is definitely internal.
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J.R. SitmanAuthor Commented:
it is a Virtual server.  How would I disconnect it?  Change the network connection to "not connected"
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J.R. SitmanAuthor Commented:
I took it off line.   The errors continued except the Account Name was always the name of the server CitrixVM_2012.   When is was online the Account Name was things like Mohamed, Robert, Sally, Admin, etc.  

So does this tell you it's internal?   If so, why does it have other Account Names when connected to the network?
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Dr. KlahnPrincipal Software EngineerCommented:
So does this tell you it's internal?   If so, why does it have other Account Names when connected to the network?

That's correct.  When it's not connected to the network, the only thing that can be attacking it is itself.

It has other account names when it is connected to the network because it can then connect to the malware master server and download lists of account names and passwords.

If it is not obvious what process is causing this, and the antivirus and anti-malware are coming up clean, then there are only two solutions:

  • Restore from a previous full backup that is known to be clean
  • Reload Windows from scratch

The second solution is ugly if there is no clean full backup, but you cannot afford to have a subverted system on your network.  At some point it will start downloading even worse malware and try to infest other systems.
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J.R. SitmanAuthor Commented:
Dr. Klahn:

I read your last post.  We are still deciding what to do.  I'll get back to you.

Thanks
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J.R. SitmanAuthor Commented:
Thanks for all the help.   We've decided to build a new server from scratch.
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J.R. SitmanAuthor Commented:
I thought it was important to update this.   Prior to building a new server I spent hours just looking for anything logical or not that could cause this.
I noticed that this VM had 2 network cards.  Only was was active.  I changed the one that was connected to "not connected".   Connected the other.  
I then checked the Event logs and all the 4625 errors had stopped.  

Why would a different IP stop the problem?
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