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

Cody Brugh cbrugh at ...2499...
Tue May 13 10:19:45 EDT 2014


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 at ...3461...>wrote:

>
>  ------------------------------
> *From:* Cody Brugh [cbrugh at ...2499...]
> *Sent:* Monday, May 12, 2014 6:30 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
>
>   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 at ...3461...
> > wrote:
>
>>
>>  ------------------------------
>> *From:* Cody Brugh [cbrugh at ...2499...]
>>
>> *Sent:* Monday, May 12, 2014 6:11 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
>>
>>   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 at ...3461...>wrote:
>>
>>>
>>>  ------------------------------
>>> *From:* Cody Brugh [cbrugh at ...2499...]
>>> *Sent:* Monday, May 12, 2014 4:32 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
>>>
>>>    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 at ...3461...
>>> > wrote:
>>>
>>>>
>>>>  ------------------------------
>>>> *From:* Cody Brugh [cbrugh at ...2499...]
>>>> *Sent:* Monday, May 12, 2014 4:11 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 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 at ...2499...> wrote:
>>>>
>>>>> Attached.
>>>>>
>>>>>
>>>>> On Mon, May 12, 2014 at 4:05 PM, Russ Combs (rucombs) <
>>>>> rucombs at ...3461...> wrote:
>>>>>
>>>>>>
>>>>>>  ------------------------------
>>>>>> *From:* Cody Brugh [cbrugh at ...2499...]
>>>>>> *Sent:* Monday, May 12, 2014 3:59 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
>>>>>>
>>>>>>    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 at ...3461...> wrote:
>>>>>>
>>>>>>>
>>>>>>>  ------------------------------
>>>>>>> *From:* Cody Brugh [cbrugh at ...2499...]
>>>>>>> *Sent:* Monday, May 12, 2014 3:01 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
>>>>>>>
>>>>>>>   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 at ...3461...> wrote:
>>>>>>>
>>>>>>>
>>>>>>>  ------------------------------
>>>>>>> *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...> wrote:
>>>>>>>
>>>>>>>>
>>>>>>>>  ------------------------------
>>>>>>>> *From:* Cody Brugh [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
>>>>>>>> *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...> 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...]
>>>>>>>> *Sent:* Monday, May 12, 2014 11:52 AM
>>>>>>>> *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
>>>>>>>>
>>>>>>>>   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...> wrote:
>>>>>>>>
>>>>>>>>>
>>>>>>>>>  ------------------------------
>>>>>>>>> *From:* Cody Brugh [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
>>>>>>>>> *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...> wrote:
>>>>>>>>>
>>>>>>>>>>  What are your shutdown / usr1 stats?  Do they show normalizer
>>>>>>>>>> blocks?
>>>>>>>>>>
>>>>>>>>>>  ------------------------------
>>>>>>>>>> *From:* Cody Brugh [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
>>>>>>>>>>
>>>>>>>>>> *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...>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 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
>>>>>>>>>>>> *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...>
>>>>>>>>>>>> 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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>>>>>>>>>>>>
>>>>>>>>>>>>  _______________________________________________
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>>>>>>>>>>>> Snort-devel at lists.sourceforge.net
>>>>>>>>>>>> https://lists.sourceforge.net/lists/listinfo/snort-devel
>>>>>>>>>>>> Archive:
>>>>>>>>>>>>
>>>>>>>>>>>> http://sourceforge.net/mailarchive/forum.php?forum_name=snort-devel
>>>>>>>>>>>>
>>>>>>>>>>>> Please visit http://blog.snort.org for the latest news about
>>>>>>>>>>>> Snort!
>>>>>>>>>>>>
>>>>>>>>>>>>
>>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>
>>>>>>>>
>>>>>>>
>>>>>>
>>>>>
>>>>
>>>
>>
>
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