Re: Rule is triggering when read from pcap but not during live capture

["Bryant, Alex B. (CDC/OCOO/OCIO)" <ize1 () cdc gov>]

James,

I found that suggestion just a few minutes ago from someone else having this problem in 2010. Just restarted Snort like 
this:

/usr/sbin/snort -A fast -b -N -D -I -i eth1 -u snort -g snort -c /etc/snort/snort.conf -y -k none -l /var/log/snort

...unfortunately, it didn't help :-(

Thanks
--Alex

-----Original Message-----
From: James Lay [mailto:jlay () slave-tothe-box net] 
Sent: Tuesday, November 03, 2015 12:47 PM
To: snort-users () lists sourceforge net
Subject: Re: [Snort-users] Rule is triggering when read from pcap but not during live capture

On 2015-11-03 10:14 AM, Bryant, Alex B. (CDC/OCOO/OCIO) wrote:
> I implemented the following rule:
>
> alert tcp $HOME_NET any -> $HOME_NET [139,445] (msg:"POLICY-OTHER use 
> of psexec remote administration tool SMBv2"; 
> flow:to_server,established; content:"|FE|SMB"; depth:8; nocase;
> content:"|05 00|"; within:2; distance:8; 
> content:"P|00|S|00|E|00|X|00|E|00|S|00|V|00|C|00|"; fast_pattern:only; 
> metadata:service netbios-ssn; 
> reference:url,technet.microsoft.com/en-us/sysinternals/bb897553.aspx
> [1]; classtype:policy-violation; sid:30281; rev:1;)
>
> ...but in testing, the corresponding traffic only generates an alert 
> when read into Snort in a .pcap - not in production / live capture. I 
> captured the pcap on the sensor itself, using the Snort capture 
> interfact (verified several times that I'm using the right interface), 
> and when I ran the pcap through Snort, it triggered the alert.
>
> Any ideas as to why a live capture does not trigger this alert, but 
> reading in a pcap of the exact same traffic would?
>
> Thanks!
>
> --Alex

When in doubt, nuke checksums with "-k none".

James

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