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Re: Snort unable to drop packets in inline mode

From: Rishabh Shah <rishabh420 () gmail com>
Date: Sun, 22 Feb 2015 20:47:11 +0530
Hi James,

Thanks for looking in to this. In your case, the HTTP request is getting
blocked by snort. But the same is not happening in my case. Any other
command output that could help you figure out this issue?

On Sun, Feb 22, 2015 at 7:55 PM, James Lay <jlay () slave-tothe-box net> wrote:


 On Sat, 2015-02-21 at 20:04 +0530, Rishabh Shah wrote:

Hi Snort-Experts,



 I am running Snort-2.9.7 in Ubuntu 14.04.1 LTS (64-bit). Snort is unable
to drop packets, despite a drop alert being generated:

 02/21-14:48:11.602240  [Drop] [**] [1:1112111:1] you are blocked [**]
[Priority: 0] {TCP} 192.168.10.1:53013 -> 157.166.226.25:80
<http://157.166.226.25/>



 -> Following rule in snort.rules file is getting triggered for the above
alert log.

 drop tcp any any -> any 80 (msg: "you are blocked"; sid: 1112111; rev:
1;)





 ===============================================================================


 Action Stats:

      Alerts:            7 (  1.118%)

      Logged:            7 (  1.118%)

      Passed:            0 (  0.000%)

 Limits:

       Match:            0

       Queue:            0

         Log:            0

       Event:            0

       Alert:            0

 Verdicts:

       Allow:          231 ( 36.435%)

       Block:            0 (  0.000%)

     Replace:            0 (  0.000%)

   Whitelist:            0 (  0.000%)

 *  Blacklist:          394 ( 62.145%)*

      Ignore:            0 (  0.000%)

       Retry:            0 (  0.000%)


===============================================================================




Interestingly, Blacklist means getting
dropped/blocked/not-allowed-through/whatever you want to call it.  Case in
point below:

start line:
sudo snort -c snort.conf -Q --daq afpacket -i eth1:eth2 -A console -k none

[ Number of patterns truncated to 20 bytes: 0 ]
afpacket DAQ configured to inline.
Acquiring network traffic from "eth1:eth2".
Reload thread starting...
Reload thread started, thread 0x7f383d236700 (3419)

        --== Initialization Complete ==--

snort rule:
drop tcp any any -> any $HTTP_PORTS (msg:"HTTP Traffic Index Get";
content:"index"; http_uri; sid:1000003; rev:1;)

wget from remote box:
[07:09:05 $] wget http://192.168.1.73/index.html
--2015-02-22 07:09:44--  http://192.168.1.73/index.html
Connecting to 192.168.1.73:80... connected.
HTTP request sent, awaiting response... Read error (Connection reset by
peer) in headers.
Retrying.

--2015-02-22 07:09:45--  (try: 2)  http://192.168.1.73/index.html
Connecting to 192.168.1.73:80... connected.
HTTP request sent, awaiting response... Read error (Connection reset by
peer) in headers.
Retrying.

--2015-02-22 07:09:47--  (try: 3)  http://192.168.1.73/index.html
Connecting to 192.168.1.73:80... connected.
HTTP request sent, awaiting response... Read error (Connection reset by
peer) in headers.
Retrying.

tshark on ips box:
 31 2015-02-22 07:09:46.143340  192.168.1.2 -> 192.168.1.73 TCP 74
43815→80 [SYN] Seq=0 Win=29200 Len=0 MSS=1460 SACK_PERM=1 TSval=1201101
TSecr=0 WS=128
 32 2015-02-22 07:09:46.143469 192.168.1.73 -> 192.168.1.2  TCP 74
80→43815 [SYN, ACK] Seq=0 Ack=1 Win=14480 Len=0 MSS=1460 SACK_PERM=1
TSval=54730 TSecr=1201101 WS=16
 33 2015-02-22 07:09:46.144245  192.168.1.2 -> 192.168.1.73 TCP 66
43815→80 [ACK] Seq=1 Ack=1 Win=29312 Len=0 TSval=1201101 TSecr=54730
 34 2015-02-22 07:09:46.145281  192.168.1.2 -> 192.168.1.73 HTTP 186 GET
/index.html HTTP/1.1
 35 2015-02-22 07:09:46.145388 192.168.1.73 -> 192.168.1.2  TCP 66
80→43815 [ACK] Seq=1 Ack=121 Win=14480 Len=0 TSval=54731 TSecr=1201101
 36 2015-02-22 07:09:46.145893  192.168.1.2 -> 192.168.1.73 TCP 54
43815→80 [RST, ACK] Seq=121 Ack=1 Win=0 Len=0
 37 2015-02-22 07:09:49.147339  192.168.1.2 -> 192.168.1.73 TCP 74
43817→80 [SYN] Seq=0 Win=29200 Len=0 MSS=1460 SACK_PERM=1 TSval=1201852
TSecr=0 WS=128
 38 2015-02-22 07:09:49.147486 192.168.1.73 -> 192.168.1.2  TCP 74
80→43817 [SYN, ACK] Seq=0 Ack=1 Win=14480 Len=0 MSS=1460 SACK_PERM=1
TSval=55481 TSecr=1201852 WS=16
 39 2015-02-22 07:09:49.148246  192.168.1.2 -> 192.168.1.73 TCP 66
43817→80 [ACK] Seq=1 Ack=1 Win=29312 Len=0 TSval=1201852 TSecr=55481
 40 2015-02-22 07:09:49.149275  192.168.1.2 -> 192.168.1.73 HTTP 186 GET
/index.html HTTP/1.1
 41 2015-02-22 07:09:49.149381 192.168.1.73 -> 192.168.1.2  TCP 66
80→43817 [ACK] Seq=1 Ack=121 Win=14480 Len=0 TSval=55482 TSecr=1201852
 42 2015-02-22 07:09:49.150088 192.168.1.73 -> 192.168.1.2  HTTP 557
HTTP/1.1 200 OK  (text/html)
 43 2015-02-22 07:09:49.151366  192.168.1.2 -> 192.168.1.73 TCP 54
43817→80 [RST, ACK] Seq=121 Ack=1 Win=0 Len=0
 46 2015-02-22 07:09:53.153356  192.168.1.2 -> 192.168.1.73 TCP 74
43818→80 [SYN] Seq=0 Win=29200 Len=0 MSS=1460 SACK_PERM=1 TSval=1202853
TSecr=0 WS=128
 47 2015-02-22 07:09:53.153489 192.168.1.73 -> 192.168.1.2  TCP 74
80→43818 [SYN, ACK] Seq=0 Ack=1 Win=14480 Len=0 MSS=1460 SACK_PERM=1
TSval=56483 TSecr=1202853 WS=16
 48 2015-02-22 07:09:53.154244  192.168.1.2 -> 192.168.1.73 TCP 66
43818→80 [ACK] Seq=1 Ack=1 Win=29312 Len=0 TSval=1202853 TSecr=56483
 49 2015-02-22 07:09:53.155285  192.168.1.2 -> 192.168.1.73 HTTP 186 GET
/index.html HTTP/1.1
 50 2015-02-22 07:09:53.155395 192.168.1.73 -> 192.168.1.2  TCP 66
80→43818 [ACK] Seq=1 Ack=121 Win=14480 Len=0 TSval=56483 TSecr=1202854
 51 2015-02-22 07:09:53.155921  192.168.1.2 -> 192.168.1.73 TCP 54
43818→80 [RST, ACK] Seq=121 Ack=1 Win=0 Len=0

snort result using console:
02/22-07:09:46.145218  [Drop] [**] [1:1000003:1] HTTP Traffic Index Get
[**] [Priority: 0] {TCP} 192.168.1.2:43815 -> 192.168.1.73:80
02/22-07:09:49.149219  [Drop] [**] [1:1000003:1] HTTP Traffic Index Get
[**] [Priority: 0] {TCP} 192.168.1.2:43817 -> 192.168.1.73:80
02/22-07:09:53.155221  [Drop] [**] [1:1000003:1] HTTP Traffic Index Get
[**] [Priority: 0] {TCP} 192.168.1.2:43818 -> 192.168.1.73:80

and lastly, snort stats after kill:

===============================================================================
Packet I/O Totals:
   Received:           57
   Analyzed:           57 (100.000%)
    Dropped:            0 (  0.000%)
   Filtered:            0 (  0.000%)
Outstanding:            0 (  0.000%)
   Injected:           12                  <----------- injected RST I am
guessing

===============================================================================


===============================================================================
Action Stats:
     Alerts:            6 ( 10.526%)
     Logged:            6 ( 10.526%)
     Passed:            0 (  0.000%)
Limits:
      Match:            0
      Queue:            0
        Log:            0
      Event:            0
      Alert:            0
Verdicts:
      Allow:           50 ( 87.719%)
      Block:            0 (  0.000%)
    Replace:            0 (  0.000%)
  Whitelist:            0 (  0.000%)
  Blacklist:            7 ( 12.281%)
     Ignore:            0 (  0.000%)
      Retry:            0 (  0.000%)

And there ya go.

James


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-- 
Regards,
Rishabh Shah.

------------------------------------------------------------------------------
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from Actuate! Instantly Supercharge Your Business Reports and Dashboards
with Interactivity, Sharing, Native Excel Exports, App Integration & more
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