Hello,
The machine is a dual Opteron with 2GB of RAM. It runs 3 instances of snort.
Each snort process sends logs to a specific log directory. Each snort process
has its barnyard process processing its logs/alerts to the mysql DB. Each snort
process listens on its own interface. Each interface is attached to the SPAN
port of a gigabit switch.
Fabien
Joel Esler:
> How much RAM do you have in your machine?
>
> Joel
>
>
> On Tue, Nov 21, 2006 at 06:48:22PM +0100, it looks like spagno_f@ifrance.com
> sent me:
> > Hello,
> >
> > We encounter a strange problem with snort 2.6.0, Barnyard, BASE, all
> > compiled from source files.
> >
> > We have alerts which do not match the alert rules generating the alert.
> > Actually, by looking at the payload, we cannot find content we should see.
> > It seems several people already complained about this problem before,
> > without any real answer
> > (http://marc.theaimsgroup.com/?l=snort-users&m=112505975311791&w=2)
> >
> > Here is an example below.
> > We have this rule generating alerts we see in BASE :
> >
> > alert ip $EXTERNAL_NET any -> $HOME_NET any (msg:"SHELLCODE x86 NOOP";
> > content: "|90 90 90 90 90 90 90 90 90 90 90 90 90 90|"; depth: 128;
> > reference:arachnids,181; classtype:shellcode-detect; sid:648; rev:4;)
> >
> > Alert generated by this rule, in BASE :
> >
> > #(6 - 56146) [2006-09-29 15:27:22] [arachnids/181] [local/648] [snort/:648]
> > SHELLCODE x86 NOOP
> > IPv4: 172.16.5.27 -> 172.16.5.12
> > hlen=5 TOS=0 dlen=155 ID=59197 flags=2 offset=0 TTL=128 chksum=45271
> > TCP: port=3563 -> dport: 1521 flags=***AP*** seq=831827579
> > ack=2816413717 off=5 res=0 win=16370 urp=0 chksum=12348
> > Payload: length = 115
> >
> > 000 : 00 73 00 00 06 00 00 00 00 00 03 5E 98 20 80 00 .s.........^. ..
> > 010 : 00 06 00 00 00 00 00 00 00 00 01 0C 00 00 00 00 ................
> > 020 : 01 00 00 00 00 E8 03 00 00 00 00 00 00 00 00 00 ................
> > 030 : 00 00 00 00 00 00 01 01 00 00 00 00 00 00 00 00 ................
> > 040 : 01 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
> > 050 : 00 00 00 00 00 00 00 00 04 00 00 00 00 00 00 00 ................
> > 060 : 00 00 00 00 00 00 00 00 00 00 00 00 07 05 C4 05 ................
> > 070 : 31 0B 07 1..
> >
> > As you can see there is no '90' bytes, as we should see in the payload.
> >
> > This not the only rule with this problem. Others have the same problem too
> > (sometimes eevn preprocessors like http_inspect too).
> >
> > While looking at the ASCII dump.log file generated by barnyard I have also
> > came accross a similar exemple (below). For this alert, we should see a
> > "user" somewhere in the payload, but we don't :
> >
> >
> > [**] [1:2650:2] ORACLE user name buffer overflow attempt [**]
> > [Classification: Attempted User Privilege Gain] [Priority: 1]
> > [Xref => http://www.appsecinc.com/Policy/PolicyCheck62.html]
> > Event ID: 62662 Event Reference: 62662
> > 11/21/06-17:16:04.892127 172.16.0.136:34833 -> 172.16.5.12:1521
> > TCP TTL:64 TOS:0x0 ID:32755 IpLen:20 DgmLen:100 DF
> > ***AP*** Seq: 0xB700F908 Ack: 0xF1594793 Win: 0x3309 TcpLen: 32
> > TCP Options (3) => NOP NOP TS: 2796076485 835448929
> > 00 30 00 00 06 00 00 00 00 00 03 68 FB 01 00 00 .0.........h....
> > 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
> > 00 00 00 00 00 00 00 00 00 00 00 04 00 00 00 01 ................
> >
> > With this problem Snort becomes almost unusable since, when we try to
> > analyse an alert to see if this is a false positive or not, we cannot have
> > the correct payload which generated the alert. We don't know if this is a
> > Snort or a Barnyard problem. Unfortunately, for now, I was not able to do a
> > tcpdump of one of these packets.
> >
> > Have you noticed the same behavior ?
> >
> > What could be the cause of the problem ? What solution to apply ?
> >
> > Thank you for your help
> >
> >
> > ________________________________________________________________________
> > iFRANCE, exprimez-vous !
> > http://web.ifrance.com
>
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> +---------------------------------------------------------------------+
> joel esler senior security consultant 1-706-627-2101
> Sourcefire Security for the /Real/ World -- http://www.sourcefire.com
> Snort - Open Source Network IPS/IDS -- http://www.snort.org
> gpg key: http://demo.sourcefire.com/jesler.pgp.key
> +---------------------------------------------------------------------+
>
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