[Snort-users] Web servers scanning clients!!!
mkettler at ...4108...
Thu Dec 26 19:34:02 EST 2002
Ahh, so sorry, I interpreted you as asking intently about target_limit, not
targets_max.. Which would, really, not matter :)
In any event both scanners_max, and targets_max are at least one order of
magnitude greater than the total number of used IPs inside this network.
(ie: there's less than 320 active systems/appliances with IP addresses here).
Even during quiescent hours when nobody else is here I can make the alerts
fire. Like right now.. yes, there are a couple of servers here, including a
DNS server, running amok, but the network is relatively quiet at the moment
and I'm the only human at a computer or making any client systems do much.
A short run of tcpdump on the snort box showed 52 packets in 19.5 seconds
(while I was not browsing the web)
[**] [117:1:1] (spp_portscan2) Portscan detected from 126.96.36.199: 1
targets 61 ports in 7 seconds [**]
12/26-22:31:34.021685 188.8.131.52:80 -> xx.xx.xx.xx:1321
TCP TTL:45 TOS:0x0 ID:8401 IpLen:20 DgmLen:48 DF
***A**S* Seq: 0x685A5A64 Ack: 0xAA737BF0 Win: 0x7E24 TcpLen: 28
TCP Options (4) => MSS: 1404 NOP NOP SackOK
For this simple example I went to http://www.securityfocus.com/ in mozilla
(1.2.1, win32), waited 30 seconds for the original connections to time-out
(I have a 20 sec timeout set for portscan2), and did a shift-reload twice.
Poof, instant alert from 61 connections in a mere 2 page loads. Given that
the default is 20, I suspect one load would trigger that level.
At 10:10 PM 12/26/2002 -0500, Jason wrote:
>Matt Kettler wrote:
>>No, this is a port_limit exceeded issue, not a nubmer of targets issue.
>>It doesn't matter how many machines are on my lan, or if the number of
>>them is greater than targets_max. The number of targets in the alert is 1 :)
>Are you absolutely sure :-)
>I understand the situation completely. Questions are sometimes intended to
>get information as much as they are intended to get a thought rolling.
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