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Re: Fwd: Snort blocking connection but not logging the drop

From: Cody Brugh <cbrugh () gmail com>
Date: Mon, 12 May 2014 16:09:00 -0400
Attached.


On Mon, May 12, 2014 at 4:05 PM, Russ Combs (rucombs) <rucombs () cisco com>wrote:



 ------------------------------
*From:* Cody Brugh [cbrugh () gmail com]
*Sent:* Monday, May 12, 2014 3:59 PM

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

  Alright, I done that and run my command but see nothing... looking at
the console and /var/log/messages...

/usr/local/bin/snort -M -A console -q --daq afpacket -i eth2:eth3 -Q
--daq-var buffer_size_mb=2048MB -c /etc/snort/snort.conf

* Ok, do this and send the whole output file (snort.log) after stopping
with ctl-c:

/usr/local/bin/snort -A cmg --daq afpacket -i eth2:eth3 -Q --daq-var
buffer_size_mb=2048MB -c /etc/snort/snort.conf &> snort.log

 This is very odd


On Mon, May 12, 2014 at 3:24 PM, Russ Combs (rucombs) <rucombs () cisco com>wrote:



 ------------------------------
*From:* Cody Brugh [cbrugh () gmail com]
*Sent:* Monday, May 12, 2014 3:01 PM

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

  That's the thing, I don't know what rule is being hit as it doesn't
show in sborby. Is there a way to show the rule that was triggered?  Maybe
that is done with the perf monitoring stuff?

 * I can't help you with Snorby.  Since this is easy for you to
reproduce, I suggest running Snort from the command line directly, no
scripts, and no -M option.  Add -A cmg -q to your command line.  You will
see the alert.



On May 12, 2014, at 2:59 PM, "Russ Combs (rucombs)" <rucombs () cisco com>
wrote:


 ------------------------------
*From:* Cody Brugh [cbrugh () gmail com]
*Sent:* Monday, May 12, 2014 2:53 PM
*To:* Russ Combs (rucombs)
*Cc:* Joel Esler (jesler); snort-devel () 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 () cisco com>wrote:



 ------------------------------
*From:* Cody Brugh [cbrugh () gmail com]
*Sent:* Monday, May 12, 2014 12:53 PM

*To:* Russ Combs (rucombs)
*Cc:* Joel Esler (jesler); snort-devel () 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 () cisco com>
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 () gmail com]
*Sent:* Monday, May 12, 2014 11:52 AM
*To:* Russ Combs (rucombs)
*Cc:* Joel Esler (jesler); snort-devel () 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 () cisco com> wrote:



 ------------------------------
*From:* Cody Brugh [cbrugh () gmail com]
*Sent:* Monday, May 12, 2014 11:18 AM

*To:* Russ Combs (rucombs)
*Cc:* Joel Esler (jesler); snort-devel () 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 () cisco com> wrote:


 What are your shutdown / usr1 stats?  Do they show normalizer blocks?

 ------------------------------
*From:* Cody Brugh [cbrugh () gmail com]
*Sent:* Monday, May 12, 2014 10:29 AM
*To:* Russ Combs (rucombs)
*Cc:* Joel Esler (jesler); snort-devel () 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 () gmail com> wrote:


 Attached is the pcap of the 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 () cisco com> wrote:



 ------------------------------
*From:* Joel Esler (jesler)
*Sent:* Thursday, May 08, 2014 8:51 PM
*To:* Cody Brugh
*Cc:* snort-devel () lists sourceforge 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 () gmail com> wrote:

  Hi,

 Our dev team is trying to work with 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 216.52.211.91:443... 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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