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Re: Question regarding distances after a byte_jump...
From: evejou <girl () techn0ev3 net>
Date: Fri, 17 Dec 2010 01:20:29 -0500

Grr.. I suddenly realized why my signature was all messed up; my fatal
mistake was forgetting that from_beginning meant: "from the VERY BEGINNING,
from the HTTP header in my packet, which I totally forgot was there."
Suddenly all of my results make sense. :P

Thanks Joel... Sorry to bother.

Also, what's the difference (if there is any) between setting "post_offset
2" and using "distance:2"?



On Thu, Dec 16, 2010 at 7:37 PM, Joel Esler <jesler () sourcefire com> wrote:

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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-- 
---
girl () techn0ev3 net

Finché c'è vita, c'è speranza.
As long as there is life, there is hope.
------------------------------------------------------------------------------
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Register now for Lotusphere 2011 and learn how
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