[Snort-sigs] Not-ing out ports

Jason Wallace jason.r.wallace at ...2420...
Mon May 13 11:06:29 EDT 2013


On Mon, May 13, 2013 at 10:19 AM, Lay, James <james.lay at ...3513...>wrote:

> Guessing you’ll want the !25 on both ends since it’s bidirectional:****
>
> ** **
>
> alert tcp !25 any <> any !25****
>
> **
>


Isn't that first !25 in the IP address field? Wouldn't it be...

alert tcp any !25 <> any !25



>  **
>
> James****
>
> ** **
>
> *From:* John Wiltberger [mailto:johwiltb at ...2420...]
> *Sent:* Monday, May 13, 2013 5:01 AM
> *To:* snort-sigs at lists.sourceforge.net
> *Subject:* [Snort-sigs] Not-ing out ports****
>
> ** **
>
> So I have a question.  When dealing with bi-directional signatures (I
> know, they aren't ideal in the least, but sometimes you can't help who
> develops your signatures), if you choose to not-out a port (as in !<port
> number>), does snort run a boolean OR on the traffic (as in 'if source port
> != <port number OR destination port != <port number>)?
>
> Reason is, I have a signature that's header is 'alert tcp any any <> any
> !25', yet it is still alerting off of traffic over port 25.  I'm sorry if
> these seems confusing, I can't think of a better way of stating this.  Any
> thoughts?****
>
>
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