Re: Question regarding distances after a byte_jump...

[Joel Esler <jesler () sourcefire com>]

Two things that I see right away that you might want to try and make your life easier.

from_beginning's function is to start it's packet jumping at the beginning of the packet, as opposed to where your 
pointer is, and I am not sure that's what you are trying to do from reading your email.

Also, post_offset can confuse the novice, so you might want go make it simpler for you.

content:"|MM MM|"; byte_jump:3,0,relative; content:"|AA AA|"; distance:2; within:2;


From reading your email, that might be what you are trying to do, please let me know?

Joel

On Dec 16, 2010, at 5:55 PM, evejou wrote:

> > I was trying to write a signature for Snort v2.6.1.5. I have a question about using the distance/within tags after 
> > a byte_test, if that's even proper use for it.
>
> Oops. I meant, byte_jump.
>
>
>
> On Thu, Dec 16, 2010 at 5:54 PM, evejou <girl () techn0ev3 net> wrote:
> Hi,
>
> I was trying to write a signature for Snort v2.6.1.5. I have a question about using the distance/within tags after a 
> byte_test, if that's even proper use for it.
>
> Say there's a packet that looks kind of like this:
>
> MM MM OO OO OO [....] TT XX XX AA AA ...
>
> (MM -- magic number)
> (OO -- offset value that points to the TTs; this offset counts from the beginning of the file)
> (XX XX -- 2 bytes that I don't care about)
>
> I was trying to figure out where the pointer would be after a byte_jump, so I tried to write the following to see if 
> it would trigger:
>       content:"|MM MM|"; byte_jump:3,0,relative,from_beginning,post_offset 2; content:"|AA AA|"; distance:0; within:2;
> I noticed that this didn't trigger, but that it did when I removed the "within:2" part.
>
>
> And then I tried the following:
>       content:"|MM MM|"; byte_jump:3,0,relative,from_beginning,post_offset 2; content:"|OO OO OO|"; distance:0; 
> within:3;
> and this triggered as well.
>
> My first question is whether this is expected behavior (or am I doing something wrong?), and adjunctly to that, how I 
> could get a hit on that second content tag (the |AA AA| part)...
>
>
> Thanks,
> Alice
>
> -- 
> ---
> girl () techn0ev3 net
>
> Finché c'è vita, c'è speranza.
> As long as there is life, there is hope. 
>
>
>
> -- 
> ---
> girl () techn0ev3 net
>
> Finché c'è vita, c'è speranza.
> As long as there is life, there is hope. 
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