[Snort-devel] Fwd: Snort blocking connection but not logging the drop

Russ Combs (rucombs) rucombs at ...3461...
Mon May 12 14:59:38 EDT 2014


________________________________
From: Cody Brugh [cbrugh at ...2499...]
Sent: Monday, May 12, 2014 2:53 PM
To: Russ Combs (rucombs)
Cc: Joel Esler (jesler); snort-devel at lists.sourceforge.net
Subject: Re: [Snort-devel] Fwd: Snort blocking connection but not logging the drop

I just disabled the tcp normalize and cleaned up some pre-processeors that I don't need, however I am still being dropped when trying to connect to the API with snort ON.  Attached are the stats from a quick run where I tried to connect 4-5 times.  Let me know if you see something or other suggestions.

* You have 1 alert, 2 blocks, 1 blacklisted, and 2 injects.  I would start by changing the rule that is firing from drop to alert.

Thanks,
Cody


On Mon, May 12, 2014 at 1:05 PM, Russ Combs (rucombs) <rucombs at ...3461...<mailto:rucombs at ...3461...>> wrote:

________________________________
From: Cody Brugh [cbrugh at ...2499...<mailto:cbrugh at ...2499...>]
Sent: Monday, May 12, 2014 12:53 PM

To: Russ Combs (rucombs)
Cc: Joel Esler (jesler); snort-devel at lists.sourceforge.net<mailto:snort-devel at lists.sourceforge.net>
Subject: Re: [Snort-devel] Fwd: Snort blocking connection but not logging the drop

What all is the normalizer used for?  Will turning it off make me vulnerable?

* The normalizer does various scrubbing and blocking to improve detection.  You need to assess your security position with or without it.  For details on the normalizer, check here:  http://manual.snort.org/node168.html.

Just trying to understand what that mechanism does.

Thanks,
Cody

On May 12, 2014, at 12:02 PM, "Russ Combs (rucombs)" <rucombs at ...3461...<mailto:rucombs at ...3461...>> wrote:

The normalizer is blocking packets:

             tcp::block: 272

You can prevent that by commenting out the normalize_tcp line from your conf.

You can debug it a little further by enabling all preprocessor rules by adding / uncommenting them in your conf or by adding this to your conf:

    config autogenerate_preprocessor_decoder_rules

Then you should see why the normalizer is blocking.  When I do that with the pcap you sent I see a bad TCP reset.

________________________________
From: Cody Brugh [cbrugh at ...2499...<mailto:cbrugh at ...2499...>]
Sent: Monday, May 12, 2014 11:52 AM
To: Russ Combs (rucombs)
Cc: Joel Esler (jesler); snort-devel at lists.sourceforge.net<mailto:snort-devel at lists.sourceforge.net>
Subject: Re: [Snort-devel] Fwd: Snort blocking connection but not logging the drop

Attached is the shutdown stats.  Let me know what you find/suggest.

Thanks,
Cody


On Mon, May 12, 2014 at 11:41 AM, Russ Combs (rucombs) <rucombs at ...3461...<mailto:rucombs at ...3461...>> wrote:

________________________________
From: Cody Brugh [cbrugh at ...2499...<mailto:cbrugh at ...2499...>]
Sent: Monday, May 12, 2014 11:18 AM

To: Russ Combs (rucombs)
Cc: Joel Esler (jesler); snort-devel at lists.sourceforge.net<mailto:snort-devel at lists.sourceforge.net>
Subject: Re: [Snort-devel] Fwd: Snort blocking connection but not logging the drop

How do I gather those stats?  Are you looking for this?  http://manual.snort.org/node20.html

* Not those.  Do a clean start, run your traffic, and then stop Snort or give it a usr1 signal and check the output.  Check console or syslog depending on how you run.

Thanks,
Cody


On Mon, May 12, 2014 at 11:05 AM, Russ Combs (rucombs) <rucombs at ...3461...<mailto:rucombs at ...3461...>> wrote:
What are your shutdown / usr1 stats?  Do they show normalizer blocks?

________________________________
From: Cody Brugh [cbrugh at ...2499...<mailto:cbrugh at ...2499...>]
Sent: Monday, May 12, 2014 10:29 AM
To: Russ Combs (rucombs)
Cc: Joel Esler (jesler); snort-devel at lists.sourceforge.net<mailto:snort-devel at lists.sourceforge.net>

Subject: Re: [Snort-devel] Fwd: Snort blocking connection but not logging the drop

Can you confirm you received my PCAP file?  I would really like to get this issue resolved so I can work with their API.

Let me know the status please.


On Fri, May 9, 2014 at 9:02 AM, Cody Brugh <cbrugh at ...2499...<mailto:cbrugh at ...2499...>> wrote:
Attached is the pcap of the stamps.com<http://stamps.com> packet capture... can someone check and see what I should do?

Thanks,
Cody


On Fri, May 9, 2014 at 8:19 AM, Russ Combs (rucombs) <rucombs at ...3461...<mailto:rucombs at ...3461...>> wrote:

________________________________
From: Joel Esler (jesler)
Sent: Thursday, May 08, 2014 8:51 PM
To: Cody Brugh
Cc: snort-devel at lists.sourceforge.net<mailto:snort-devel at ...2402...net>
Subject: Re: [Snort-devel] Fwd: Snort blocking connection but not logging the drop

Can you send your configuration file, and a packet capture of the session?

* Can you also send your usr1 / shutdown stats?


--
Joel Esler
Sent from my iPhone

On May 8, 2014, at 20:49, "Cody Brugh" <cbrugh at ...2499...<mailto:cbrugh at ...1067...2499...>> wrote:

Hi,

Our dev team is trying to work with stamps.com<http://stamps.com> API however our in-line snort box is blocking the return connection for unknown reasons.  When I turn off snort the connection flows perfectly.  Looking at snorby I see no event of the connection being dropped.  I've included the command we are running from a internal server that is behind the snort.  I also included the tcpdump from this same server for the connection.

wget https://216.52.211.91/label/health.aspx
--2014-05-08 20:37:33--  https://216.52.211.91/label/health.aspx
Connecting to 216.52.211.91<tel:216.52.211.91>:443... connected.


20:37:33.443962 IP 10.2.2.1.52661 > 216.52.211.91.443: Flags [F.], seq 3298140140, ack 2463587275, win 8208, options [nop,nop,TS val 2824990869 ecr 3731400338], length 0
20:37:33.444478 IP 216.52.211.91.443 > 10.2.2.1.52661: Flags [R.], seq 1, ack 1, win 8208, length 0
20:37:33.989510 IP 10.2.2.1.59800 > 216.52.211.91.443: Flags [S], seq 3306929108, win 65535, options [mss 1460,nop,wscale 3,sackOK,TS val 2824990923 ecr 0], length 0
20:37:34.071548 IP 216.52.211.91.443 > 10.2.2.1.59800: Flags [S.], seq 361712399, ack 3306929109, win 4140, options [mss 1380,nop,wscale 3,nop,nop,TS val 3731482846 ecr 2824990923,sackOK,eol], length 0
20:37:34.071610 IP 10.2.2.1.59800 > 216.52.211.91.443: Flags [.], ack 1, win 8208, options [nop,nop,TS val 2824990932 ecr 3731482846], length 0
20:37:34.071750 IP 10.2.2.1.59800 > 216.52.211.91.443: Flags [P.], ack 1, win 8208, options [nop,nop,TS val 2824990932 ecr 3731482846], length 139
20:37:34.154367 IP 216.52.211.91.443 > 10.2.2.1.59800: Flags [.], ack 140, win 517, options [nop,nop,TS val 3731482928 ecr 2824990932], length 1368
20:37:34.154462 IP 216.52.211.91.443 > 10.2.2.1.59800: Flags [.], ack 140, win 517, options [nop,nop,TS val 3731482928 ecr 2824990932], length 1368
20:37:34.154490 IP 10.2.2.1.59800 > 216.52.211.91.443: Flags [.], ack 2737, win 7877, options [nop,nop,TS val 2824990940 ecr 3731482928], length 0

20:37:44.153373 IP 216.52.211.91.443 > 10.2.2.1.59800: Flags [R.], seq 4233:4288, ack 140, win 534, length 55

any help or suggestions would be great, I would like to disable the rule that is blocking this connection but like I said I cannot see which rule blocked it.

Thanks.


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