Re: What's going on here?

From: wykkydat_private
Date: Thu Aug 29 2002 - 11:21:07 PDT

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    In-Reply-To: <000f01c24eb9$2837b150$841e0a0a@dynamite>
    >Don't know if this was mentioned, haven't been following the whole thread,
    >but my suggestion would be that it's someone who physically resides in 
    >upstream path portscanning, using source port 80 to fool misconfigured
    >non-stateful ACLs into thinking that these are replies to normal web
    >traffic, but using Syn only to catch valid open TCP ports.
    >-Mark C.
    Here's my guess (as that is truly all I can do with the information given).
    Three scenarios, both based on the facts that (1) ZoneAlarm is host-based, 
    ans (2) 10.x is not an internet-routable protocol (as in, no router will 
    forward it outside of your own network):
    Scenarion #1:  Someone port scanning your system:
    IF it was a port scan, how would the SYN-ACKs be routed back to the 
    scanner (source)?  Someone external to your network would receive no 
    results by spoofing these IPs (if that is what it is) because the 
    responses wouldn't be routed properly (see Scenario #2, below).
    Coming from a 10.x IP, it would have to someone INSIDE your own network 
    doing the scanning, assuming you use NAT behind your firewall (so that 
    folks would HAVE a 10.x IP to begin with), for any measurable results to 
    come from the scanning.  
    Bottom line:  IF it is port scanning, it is from the inside (or the person 
    on the outside is silly).
    Scenario #2:  Someone attempting to DoS your system:
    IF it is a DoS, by continually scanning your system with non-routable IPs, 
    if will cause you to consume system resources by waiting for time-outs or 
    other nastiness to occur.  The fallacy of this plan, though, is that they 
    are hitting seemingly random ports, which will make the DoS effect (IF 
    that is what this was) less, and easier for your system to process.  If 
    they were to hit a single port known to be open on your system, the 
    ensuing SYN-ACKs would take longer to get error messages, thus taking more 
    system resources, and tying up more "wait-states".
    Bottom Line:  IF it is DoS, it is a poor one, at best, and probably 
    Scenario #3:  This is the combo scenario (allow me to explain)...
    IF you have a misconfigured network device, say, your firewall, and it is 
    performing NAT INBOUND (as opposed to only outbound) it could be masking 
    the scanner's true IP.  In this case, this could be a combination of a 
    misconfigured NATing device and one of the two scenarios above.
    Bottom Line:  Make sure your network firewall is not performing INBOUND 
    Network Address Translation!!!
    Others can probably come up with other solutions (I kind of like the ad 
    server one, but how would a 10.x IP be routed across the internet again, 
    unless it was spoofed, and ad servers don't generally do that) but this is 
    what I came up with (as in, if I was doing for you what I get paid to do 
    for other people (network forensics)) these are what I would pursue 
    Good luck.
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