[Snort-users] snort suddenly stopped to record events

Alex linux at ...14373...
Wed Jul 24 10:00:18 EDT 2013


Hi Waldo,

Thanks again for your help. I've collected more info, see below :-)

just commenting out UDP rules in /etc/snort/rules/local-test.rules:

#alert udp $EXTERNAL_NET any -> $HOME_NET any (msg:"udp traffic inbound"; 
classtype:misc-activity; sid:5; rev:1;)
#alert udp $HOME_NET any -> $EXTERNAL_NET any (msg:"udp traffic outbound"; 
classtype:misc-activity; sid:6; rev:1;)

will still continue to log UDP packets in syslog!!!!

Jul 24 13:56:14 ids snort: [1:4:1] ip traffic outbound [Classification: 
Unknown Traffic] [Priority: 3] {UDP} 192.168.51.10:138 -> 192.168.51.255:138
Jul 24 13:56:14 ids snort: [1:3:1] ip traffic inbound [Classification: 
Unknown Traffic] [Priority: 3] {UDP} 192.168.51.10:138 -> 192.168.51.255:138

Commenting out also ip rules in /etc/snort/rules/local-test.rules, will 
cause snort to stop logging UDP packets.

#alert ip $EXTERNAL_NET any -> $HOME_NET any (msg:"ip traffic inbound"; 
classtype:unknown; sid:3; rev:1;)
#alert ip $HOME_NET any -> $EXTERNAL_NET any (msg:"ip traffic outbound"; 
classtype:unknown; sid:4; rev:1;)

but this time, in merged.log, nothing is recorded! To isolate somehow the 
problem:

- on one terminal I've started a tcpdump -v tcp -i eth4
- on second terminal, i've started: snort -u snort -g snort snort -c 
/etc/snort/snort.conf

on my host (192.168.51.59) I've telneted host 192.168.51.61 on port 80 
(which is a network printer) and has a management interface listening on 
port 80

See below logs:
[root at ...4157... ~]# tcpdump -v -nn tcp -i eth4
tcpdump: WARNING: eth4: no IPv4 address assigned
tcpdump: listening on eth4, link-type EN10MB (Ethernet), capture size 96 
bytes
14:51:45.701106 IP (tos 0x0, ttl  64, id 27972, offset 0, flags [DF], proto: 
TCP (6), length: 48) 192.168.51.61.80 > 192.168.51.59.1984: S, cksum 0xf7ba 
(correct), 3548862483:3548862483(0) ack 3068431451 win 11680 <mss 
1460,nop,wscale 0>
14:51:45.702054 IP (tos 0x0, ttl  64, id 0, offset 0, flags [DF], proto: TCP 
(6), length: 40) 192.168.51.61.80 > 192.168.51.59.1984: R, cksum 0x946b 
(correct), 3548862484:3548862484(0) win 0

[root at ...4157... snort]# tail -f /var/log/messages|grep snort
Jul 24 14:51:45 ids snort: [1:2:1] tcp traffic outbound [Classification: A 
TCP connection was detected] [Priority: 4] {TCP} 192.168.51.61:80 -> 
192.168.51.59:1984
Jul 24 14:51:45 ids snort: [1:1:1] tcp traffic inbound [Classification: A 
TCP connection was detected] [Priority: 4] {TCP} 192.168.51.61:80 -> 
192.168.51.59:1984
Jul 24 14:51:45 ids snort: [1:2:1] tcp traffic outbound [Classification: A 
TCP connection was detected] [Priority: 4] {TCP} 192.168.51.61:80 -> 
192.168.51.59:1984
Jul 24 14:51:45 ids snort: [1:1:1] tcp traffic inbound [Classification: A 
TCP connection was detected] [Priority: 4] {TCP} 192.168.51.61:80 -> 
192.168.51.59:1984

Now, I have a question, to be sure that I am understanding correctly snort 
functionality.

Supposing that barnyard IS NOT STARTED and udp and ip rules are enabled in 
local-test.rules, I am able to see that in merged.log will be recorderded 
some things and also in syslog will appear alerts!!!!

Now, in snort.conf I have 2 lines defined for output:

output unified2: filename merged.log, limit 128

and

output alert_syslog: LOG_AUTH LOG_ALERT


What line in snort.conf will produce alerts in syslog?


As far as I understand, output unified2: filename merged.log, is related to 
barnyard and will not record in syslog.

ONLY when barnyard2 will be started, merged.log file will be read and in 
case will be some alerts, barbyard2 will write them in syslog. Correct?

The second line (output alert_syslog: LOG_AUTH LOG_ALERT), will be 
responsible to write direct in syslog and has nothing to do with merged.log 
file above. Right?

So answer to my question above is: output alert_syslog: LOG_AUTH LOG_ALERT! 
Right?

Now, I've started snort as daemon and tried to generate some traffic again, 
telneting another host from the same source (192.168.51.59)

telnet 192.168.51.100 80! Unfortunatelly, this time tcpdump will show and 
record only arp request:

[root at ...4157... ~]# tcpdump -i eth4 -v host 192.168.51.59
tcpdump: WARNING: eth4: no IPv4 address assigned
tcpdump: listening on eth4, link-type EN10MB (Ethernet), capture size 96 
bytes
16:20:41.672663 arp who-has 192.168.51.59 tell 192.168.51.100

and this event is not recorded/alerted by snort even connection has been 
established. Is this normal?

Anyway, in this time, something has been recorded in merged.log file. I've 
decoded using u2spewfoo, see blelow:

[root at ...4157... eth4]# ./u2spewfoo merged.log.1374667559
(Event)
        sensor id: 0    event id: 1     event second: 1374667574 
event microsecond: 908616
        sig id: 8       gen id: 1       revision: 1      classification: 31
        priority: 3     ip source: 192.168.51.1 ip destination: 
192.168.51.49
        src port: 3     dest port: 13   protocol: 1     impact_flag: 0 
blocked: 0

Packet
        sensor id: 0    event id: 1     event second: 1374667574
        packet second: 1374667574       packet microsecond: 908616
        linktype: 1     packet_length: 118
[    0] B8 27 EB 34 9D 90 00 0C 42 BD 73 44 08 00 45 C0  .'.4....B.sD..E.
[   16] 00 68 E4 77 00 00 40 01 AD DA C0 A8 33 01 C0 A8  .h.w.. at ...16454...
[   32] 33 31 03 0D A3 13 00 00 00 00 45 C0 00 4C 00 00  31........E..L..
[   48] 40 00 3F 11 95 0A C0 A8 33 31 C1 E6 F0 16 00 7B  @.?.....31.....{
[   64] 00 7B 00 38 93 37 23 03 0A EC 00 00 11 E3 00 13  .{.8.7#.........
[   80] BB 0A C1 E6 F0 16 D5 86 49 8C 95 67 7C 2B D5 86  ........I..g|+..
[   96] 49 8C 94 62 D4 0A D5 86 49 8C 95 67 7C 2B D5 9A  I..b....I..g|+..
[  112] 41 B4 91 18 87 57                                A....W

(Event)
        sensor id: 0    event id: 2     event second: 1374667574 
event microsecond: 908616
        sig id: 7       gen id: 1       revision: 1      classification: 31
        priority: 3     ip source: 192.168.51.1 ip destination: 
192.168.51.49
        src port: 3     dest port: 13   protocol: 1     impact_flag: 0 
blocked: 0

Packet
        sensor id: 0    event id: 2     event second: 1374667574
        packet second: 1374667574       packet microsecond: 908616
        linktype: 1     packet_length: 118
[    0] B8 27 EB 34 9D 90 00 0C 42 BD 73 44 08 00 45 C0  .'.4....B.sD..E.
[   16] 00 68 E4 77 00 00 40 01 AD DA C0 A8 33 01 C0 A8  .h.w.. at ...16454...
[   32] 33 31 03 0D A3 13 00 00 00 00 45 C0 00 4C 00 00  31........E..L..
[   48] 40 00 3F 11 95 0A C0 A8 33 31 C1 E6 F0 16 00 7B  @.?.....31.....{
[   64] 00 7B 00 38 93 37 23 03 0A EC 00 00 11 E3 00 13  .{.8.7#.........
[   80] BB 0A C1 E6 F0 16 D5 86 49 8C 95 67 7C 2B D5 86  ........I..g|+..
[   96] 49 8C 94 62 D4 0A D5 86 49 8C 95 67 7C 2B D5 9A  I..b....I..g|+..
[  112] 41 B4 91 18 87 57                                A....W

Which decoded with u2boat and tcpdump mean:

[root at ...4157... eth4]# ./u2boat merged.log.1374667559 dump.alx
Defaulting to pcap output.

[root at ...4157... eth4]# tcpdump -r dump.alx
reading from file dump.alx, link-type EN10MB (Ethernet)
15:06:14.908616 IP 192.168.51.1 > 192.168.51.49: ICMP host 193.230.240.22 
unreachable - admin prohibited filter, length 84
15:06:14.908616 IP 192.168.51.1 > 192.168.51.49: ICMP host 193.230.240.22 
unreachable - admin prohibited filter, length 84
[root at ...4157... eth4]#

So, I think it matched with your test/debug rules found in 
/etc/snort/rules/local-test.rules

alert icmp $EXTERNAL_NET any -> $HOME_NET any (msg:"icmp traffic inbound"; 
classtype:icmp-event; sid:7; rev:1;)
alert icmp $HOME_NET any -> $EXTERNAL_NET any (msg:"icmp traffic outbound"; 
classtype:icmp-event; sid:8; rev:1;)

If I'm turning off your debug rules, snort (with all rules updated daily 
using pulledpork), will not log anything!!!

So, where is the mistake/problem? In case you need more infor or want to see 
content of any other directory or file on my computer, just let me know ...

Regards,
Alx
----- Original Message ----- 
From: "waldo kitty" <wkitty42 at ...14940...>
To: <snort-users at lists.sourceforge.net>
Sent: Tuesday, July 23, 2013 7:12 PM
Subject: Re: [Snort-users] snort suddenly stopped to record events


> On 7/23/2013 04:02, linux at ...14373... wrote:
>> Hi Waldo,
>>
>> Thanks for help :-). Tried provided debug rules and snort is working and 
>> logging
>> events but only for UDP!!!
>>
>> Seems that something is missconfigured in my snort.conf file or some 
>> existent
>> rules is blocking snort to log and alert. I am attaching here my 
>> snort.conf
>> file, maybe you can identify what is wrong or you have a suggestion.
>
> everything posted looked ok... i don't see anything that jumps out in your
> snort.conf, either... you ran snort for just over 2 minutes (129.124889 
> seconds)
> and processed 310 packets... it is possible that there was no TCP packets 
> during
> that time...
>
> try this...
>
> 1. edit local-test.rules
> 2. comment out the two UDP rules
> 3. save and exit
> 4. edit snort.conf
> 5. enable local-test.rules
> 6. save and exit
> 7. restart snort
>
> now generate some TCP traffic... browsing to a web site should work...
>
> does that TCP traffic show up now?
>
> don't forget to edit your snort.conf to disable local-test.rules when you 
> finish
> running each set of tests... you really don't want snort to be grabbing
> everything... the logs can get monstrously huge ;)
>
> -- 
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