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

From: Cody Brugh <cbrugh () gmail com>
Date: Tue, 13 May 2014 10:36:28 -0400
Attached is the info you requested.... I included tcpdump from a server
successfully connecting to the API with snort OFF.

Also is attached is the PCAP for when snort is ON and the packet being
dropped.

Let me know the next steps.



On Tue, May 13, 2014 at 10:19 AM, Cody Brugh <cbrugh () gmail com> wrote:


Quick question on the "passive mode"... we use a bypass switch that checks
snort heartbeat... if I set snort to passive mode the bypass switch doesn't
flow traffic through the snort box at all.  This means the packet captures
for the passive mode will need ran from a server itself, is that fine?



On Tue, May 13, 2014 at 9:51 AM, Russ Combs (rucombs) <rucombs () cisco com>wrote:



 ------------------------------
*From:* Cody Brugh [cbrugh () gmail com]
*Sent:* Monday, May 12, 2014 6:30 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

  Ok, I disabled everything (rules, normalizations, pre-processors,
dynamic rules) and still not able to connect  with snort in-line.

 Attached is my snort.conf to make sure I got everything... At this point
do you believe this is a bug?  Would the alpha snort version maybe work?

 * Not clear what is going on, but with everything disabled, changing
versions shouldn't make a difference.

 Please send:

 -- Snort configure line (./configure ... )
-- Snort command line
-- Snort conf
-- pcap with one successful connection while running Snort in passive mode
-- pcap with one unsuccessful connection while running Snort in inline
mode
-- snort-passive.log and snort-inline.log

 Based on the earlier emails, the commands to generate the logs are
these:

     snort -A cmg --daq afpacket -i eth2:eth3 --daq-var
buffer_size_mb=2048MB \
         -c /etc/snort/snort.conf &> snort-passive.log

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

 The pcaps should be captured for each of the above runs.

 You can send directly to me if anything is sensitive.

 Thanks
Russ

  On Mon, May 12, 2014 at 6:19 PM, Russ Combs (rucombs) <
rucombs () cisco com> wrote:



 ------------------------------
*From:* Cody Brugh [cbrugh () gmail com]

*Sent:* Monday, May 12, 2014 6:11 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

  Would a pre-processor engine be blocking but not logging?  When you
say disable things are you talking about removing pre-processing engines or
other?

 * The are two ways packets get blocked: rules and normalization.  If
those aren't indicated, it could be a bug or it could be something else
entirely, like your Snort environment.  To isolate, first disable all your
rules.  Then disable all normalizations.  Then start disabling
preprocessors.


On Mon, May 12, 2014 at 6:06 PM, Russ Combs (rucombs) <rucombs () cisco com

wrote:




 ------------------------------
*From:* Cody Brugh [cbrugh () gmail com]
*Sent:* Monday, May 12, 2014 4:32 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

   Running in passive mode I see no alerts/blocks for this specefic
API command... Also note that the API command is running without a problem
now that snort is in passive mode.

 Something inside of snort is catching it but I cannot figure out
what... would this be like a preprocessor or dynamic rules or something?

 * If there is something in Snort blocking your session, then the
output should indicate that.  At this point I would try disabling things
systematically to isolate it.


On Mon, May 12, 2014 at 4:18 PM, Russ Combs (rucombs) <
rucombs () cisco com> wrote:



 ------------------------------
*From:* Cody Brugh [cbrugh () gmail com]
*Sent:* Monday, May 12, 2014 4:11 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 now see my other alerts/drops coming in on the console, however
when I run the API command I get nothing from a alert/drop status...  What
else could be blocking it?

 * The log you sent shows no blocks, so either it isn't configured the
same or it isn't getting the same traffic as before.  Or maybe you have
more than one Snort running?  In any case, the output you sent indicates
Snort is not the problem.

What happens if you run in passive mode by just removing the -Q?  Do
you get alerts?  Blocks?


On Mon, May 12, 2014 at 4:09 PM, Cody Brugh <cbrugh () gmail com> wrote:


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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