Re: sfPortscan - false positive

[Izik Birka <Izik.Birka () hot net il>]

I have EXCH server , hosts are communicate with him with different ports ,because of that  this is trigging  alarm
I can add the EXCH server ip to the ignored_scanned option , but then if someone will scan my EXCH I will not receive 
alarm
This case is happening  with many servers in my environment ... and I need to ignored them all

It's pretty bummer .....

Thanks
Izik Birka


From: Y M [mailto:snort () outlook com]
Sent: Sunday, February 21, 2016 6:09 PM
To: Izik Birka <Izik.Birka () hot net il>
Cc: snort-users () lists sourceforge net
Subject: RE: [Snort-users] sfPortscan - false positive

In this case you need to look at your network traffic using tcpdump or something else and see what's causing the FPs. 
There are plenty of situations where misconfigured devices, network or otherwise, can lead to such behavior. Analyze 
and tweak further.

I am not sure what do you mean by "not good enough". Thresholding should take care of it if configured properly.

Another option is to "abuse" the reputation preprocessor and its whitelist. Though I haven't used this preprocessor for 
this purpose. YMMV.

As for the suppression, you need to create one for each. As far as I recall, it's always been the case. Anyone, correct 
if I am wrong.

YM
_____________________________
From: Izik Birka <izik.birka () hot net il<mailto:izik.birka () hot net il>>
Sent: Sunday, February 21, 2016 6:58 PM
Subject: RE: [Snort-users] sfPortscan - false positive
To: Y M <snort () outlook com<mailto:snort () outlook com>>
Cc: <snort-users () lists sourceforge net<mailto:snort-users () lists sourceforge net>>



Yes,
I'm familiar with this manuals but it still not good enough , in addition  I can't configure src and dst  both for 
suppression

Thanks
Izik Birka

From: Y M [mailto:snort () outlook com]
Sent: Sunday, February 21, 2016 5:43 PM
To: Izik Birka <Izik.Birka () hot net il<mailto:Izik.Birka () hot net il>>
Cc: snort-users () lists sourceforge net<mailto:snort-users () lists sourceforge net>
Subject: Re: [Snort-users] sfPortscan - false positive


For thresholding, check this: http://manual.snort.org/node35.html

For suppression check this: http://manual.snort.org/node207.html


As you will note, these do not operate at the port level, its a combination of sid / gid / src or dst IP.



YM

________________________________
From: Izik Birka <Izik.Birka () hot net il<mailto:Izik.Birka () hot net il>>
Sent: Sunday, February 21, 2016 3:35 PM
To: Y M
Cc: snort-users () lists sourceforge net<mailto:snort-users () lists sourceforge net>
Subject: RE: [Snort-users] sfPortscan - false positive


This is my configuration



# Portscan detection.  For more information, see README.sfportscan

preprocessor sfportscan: proto  { all } \

                          memcap { 10000000<tel:10000000> } \

                          sense_level { low } \

                          ignore_scanners { IP,IP,IP } \

                          ignore_scanned { IP,IP/24,IP,IP/24, IP,IP,IP } \

                                scan_type { portscan }







as you can see I configured scan_type  and I start to Exclude IPs than I realize that it's going to be a hard work so I 
stast searching for better solution ,

what can I configured in the thresholding file ?



I want for example to receive alert for 10 ports attempted scanned  or more per ip - this will reduce a lot of my 
alerts...



From: Y M [mailto:snort () outlook com]
Sent: Sunday, February 21, 2016 4:33 PM
To: Izik Birka <Izik.Birka () hot net il<mailto:Izik.Birka () hot net il>>
Cc: snort-users () lists sourceforge net<mailto:snort-users () lists sourceforge net>
Subject: RE: [Snort-users] sfPortscan - false positive



If you review the sfportscan configurations here: http://manual.snort.org/node79.html, you can specify the scan type 
and the scan sensitivity, watch, and ignore. Portsweep is different than port scan, is just an example.
sfPortscan Configuration - SNORT Users Manual 2.9.7<http://manual.snort.org/node79.html>
manual.snort.org<http://manual.snort.org>
Format Up: sfPortscan Previous: sfPortscan Contents sfPortscan Configuration. Use of the Stream5 preprocessor is 
required for sfPortscan. Stream gives portscan ...




YM



Sent from Mobile





On Sun, Feb 21, 2016 at 6:28 AM -0800, "Izik Birka" <Izik.Birka () hot net il<mailto:Izik.Birka () hot net il>> wrote:

How this data can help me ? if I can't change the ratio

I continue to get false positive alerts



Is there any way to configure the number of scanning attempt and the time period for alert to show ?



In the past the command was bit different and I was able to configure it



Example :

Preprocessor portscan: 192.168.1.0/24 10 60

10 is the number of scanning attempt

60 is time period



Thanks

Izik Birka







From: Y M [mailto:snort () outlook com]
Sent: Sunday, February 21, 2016 4:20 PM
To: Izik Birka <Izik.Birka () hot net il<mailto:Izik.Birka () hot net il>>
Cc: snort-users () lists sourceforge net<mailto:snort-users () lists sourceforge net>
Subject: Re: [Snort-users] sfPortscan - false positive



I believe they refer to the data generated by the preprocessor. Review the distribution of the data points mentioned. I 
am not on a computer to verify.



YM



Sent from Mobile





On Sun, Feb 21, 2016 at 3:20 AM -0800, "Izik Birka" <Izik.Birka () hot net il<mailto:Izik.Birka () hot net il>> wrote:

Hi

I'm trying to tune PortScan false Positive I found this explanation in snort site



Make use of the Priority Count, Connection Count, IP Count, Port Count, IP range, and Port range to determine false 
positives.



But I didn't understand where I can change those values ,



Who knows ?



Thanks

Izik Birka

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