[Snort-users] No trace for corresponding alerts

Sheahan, Paul (PCLN-NW) Paul.Sheahan at ...2218...
Fri Oct 5 08:55:04 EDT 2001

I have two custom rules that I have always used that check for outgoing
connections on port 80 (HTTP) and 69 (TFTP). I don't check for flags because
this rarely occurs on our network anyway, so it is always caught just
looking at the destination port. Here are my two custom rules:

alert tcp $HOME_NET any -> $EXTERNAL_NET 80 (msg:"Outgoing http port 80";)
alert tcp $HOME_NET any <> $EXTERNAL_NET 69 (msg:"Outgoing tftp port 69";)

Internmittenly, these rules are met and an alert is generated. For example,
here are two alerts directly from my alerts file from yesterday (with
<internal server> replacing the actual IP address):

10/04-00:23:40.992329  [**] [1:0:0] Outgoing http port 80 [**] {TCP}
<internal server>:47873 ->
10/04-00:32:20.996684  [**] [1:0:0] Outgoing tftp port 69 [**] {TCP}
<internal server>:47873 ->

When I check the trace file, there are no corresponding traces. This problem
with traces not being created seems to be fairly new. One interesting thing
looking at the above alerts is that both have the same source port of 47873.
I would think the chances of this would be very slim. Not sure if there is
any signifigance to this though.....

Any ideas?


Paul Sheahan
Manager of Information Security
paul.sheahan at ...2218...

-----Original Message-----
From: niceshorts at ...131... [mailto:niceshorts at ...131...]
Sent: Thursday, October 04, 2001 2:54 PM
To: Snort List (E-mail)
Subject: Re: [Snort-users] No trace for corresponding alerts

Sheahan, Paul (PCLN-NW) hat geschrieben:

>I'm using Snort 1.8.1 B78 on Red Hat Linux 7.0. I use the latest version of
>snort_stat.pl to generate reports for me every night at midnight. I then
>have the report emailed to me automatically.
>For every alert, there has ALWAYS been a corresponding trace in my trace
>file. This allows me to lookup details on alerts when needed. Ever since
>upgrading to Build 78 and the latest snort_stat (both upgraded around the
>same time), maybe 10% of the time, I find no corresponding trace for a
>alert. Not sure if this is a bug in Build 78 or the latest snort_stat, but
>there is a DEFINITE problem. This worked flawlessly in the past. Has anyone
>else experienced this? 

    Post some example alerts. I've seen this problem often on
    win32 beta builds. There are some distinguishing features of
    these "phantom" alerts which I would like some correlation
    on. I don't use snort_stat so if you could cut and paste from
    alert.ids that would be great.

    -anthony kim
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