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
>
>
> ________________________________________________________________________
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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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