Snort reported UDP scans
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  1. #1
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    Question Snort reported UDP scans

    Anyone seen this type of activity?:

    On 11/29, an internal workstation appeared to perform UDP portscans to 27 unique external IPs. All the external addresses examined were foreign (mostly Brazil and Argentina, but also included Columbia, Germany, Indonesia, China, et. al.). It appears to have scanned the same IP list twice, with a couple of the IPs only appearing once in each scan (possibly due to dropped traffic on the sensor). Scans took place at 17:56 and again at 18:10. It's unclear if there were any returns on the scans. I could find no other appearances of the inside or outside IPs setting off any other alerts in the data that I have. Most of the IP addresses I looked at appeared to be customer addys from ISPs.

    On 12/3, the system's admin was contacted, who claimed to run a full-virus scan and found nothing.

    On 12/4, the same system performed the same type of scan against 11 more systems. Again, all were foreign (Mostly Brazil, a couple German, and Venezuela) -- but not a single one was a duplicate from the first scan, nor were they even within the same networks.

    Because of the kludgy portscan reporting of Snort, I cannot accurately tell which ports are being targeted. The sensor's been up/down over the last month (I was out of town) so there could have been more events...

    Ideas? (My favorite answer so far is a worm...but none detected by Symantec -- assuming the admin *did* do a scan... ;0)

  2. #2
    Jaded Network Admin nebulus200's Avatar
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    Are the UDP destination or source ports consistent? Assuming XP SP2 or Win2k3 and consistent ports, try netstat -nab, this will tell you all active connections/open/listening ports, and what programs have them open. In my experience, it is usually able to determine the source of the traffic; however, if there is a rootkit involved, your mileage may vary...

    Is the system using a local firewall?

    Is there any consistency to the times that the scans happen? Day of the week? Time of Day? Day of month?

    Tried looking through a list of running processes and cross-comparing them? (alternative tools to native OS commands might help in this respect)

    Just a few thoughts off the top of my head...
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  3. #3
    Right turn Clyde Nokia's Avatar
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    I would say it was an Nmap -D scan (decoy) - to hide/obscure the attackers real IP address he can tell Nmap to insert spoofed IP's of the attackers choosing into the probes or have Nmap use random IP's of its choosing. This way although one of the connections will be from the attackers real IP address, most of the logs will be full of spoofed IP's.

    Path tracing etc can protect against this if you want to configure it.
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  4. #4
    I'd rather be fishing DjM's Avatar
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    Have you tried running Anti-Spyware programs (Search & Destroy, Adware...etc) on this system? I have see this type of activity when this type of 'scumware' tries to phone home.

    Cheers:
    DjM

  5. #5
    Super Moderator: GMT Zone nihil's Avatar
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    Hi,

    On 11/29, an internal workstation appeared to perform UDP portscans to 27 unique external IPs.
    1. Where is this machine located?
    2. Who normally uses it?
    3. When did they logoff on those days?
    4. Is there any scanning or non-standard software on the machine?

    I am wondering if this was not an inside job? if it is a worm why haven't other machines on the network been compromised?

    Can users install/uninstall software?, use thumb drives, boot from CDs etc.?

    My suggestion is that if it isn't malware as nothing has been detected, and it isn't a self-deleting item, then it must be a regular application.

    You might try a file recovery tool to see if anything interesting has been deleted from the machine.
    If you cannot do someone any good: don't do them any harm....
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  6. #6
    Just Another Geek
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    Configure snort to, besides the 'interpreted' ascii log, also log the raw ip packets. Use the 'regular' ascii log only to read it and as a guideline. Use the logged raw packets to verify what exactly went on. Otherwise you'll always be shooting in the dark.

    The problem with (UDP) portscans is that they usually aren't. But to be sure you would need to know what really happened.

    I'd point to the relevant snort manual section but the snort site doesn't seem to like me very much today. And I don't have snort running right now.
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  7. #7
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    Good ideas. Admin claims no malware (although I'm skeptical). I'm thinking it must be a "legit" tool (users CAN install pretty much whatever they want in our university environment). The file recovery is an interesting idea...

    I've been leaving tcpdumps up listening for that IP -- attempting to correlate any/all activity should the alert trigger again -- so far, nothing... If I ever get a good handle on this, I'll post the answer, but right now I'm not so sure.

    Thanks,

  8. #8
    Super Moderator: GMT Zone nihil's Avatar
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    Hi Mykol,

    I just had a thought, although I don't know how that would fit in with portscans, as that is not my field.

    Most of the IP addresses I looked at appeared to be customer addys from ISPs.
    Could it be some sort of anonymising or multiple proxy software?

    From what you say about your environment, it may well have been run from a CD or thumb drive.

    Possibly a student working on a project?

    Just a thought.
    Last edited by nihil; December 10th, 2007 at 07:07 PM.
    If you cannot do someone any good: don't do them any harm....
    As long as you did this to one of these, the least of my little ones............you did it unto Me.
    What profiteth a man if he gains the entire World at the expense of his immortal soul?

  9. #9
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    Never found out what this was. But that's something I hadn't thought of, nihil. I saw something like this a few months ago where a user downloaded a streaming viewer -- malware alarms never went off -- but in the fine-print, it did talk about it utilizing your box as part of the network...

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