Re: question about finding out about traffic

[Matt Kettler <mkettler () evi-inc com>]

Your first-place to go should be here:

http://www.snort.org/snort-db/

enter the SID and search.

If there isn't much good information yet, check the reference links (if 
those are populated).

648 does not yet have a full description, but does have an arachnids 
reference link with good information.

You can also try digging through the archives of the snort-sigs mailing 
list, which for SID 648 yields this submission that has not yet made it to 
the web database. (I searched my local archive, since I subscribe, but I 
believe there is a web archive).

--
Rule:
alert ip $EXTERNAL_NET any -> $HOME_NET any (msg:"SHELLCODE x86 NOOP";
content: "|90 90 90 90 90 90 90 90 90 90 90 90 90 90|"; depth: 128;
reference:arachnids,181; classtype:shellcode-detect; sid:648; rev:4;)

--
Sid:
648

--
Summary:
A series of NOP instructions for Intel's x86 architecure was detected.

--
Impact:
As part of an attack on a remote service, an attacker may attempt to
take advantage of insecure coding practices in hopes of executing
arbitrary code.  This procedure generally makes use of NOPs.

--
Detailed Information:
The NOP allows an attacker to fill an address space with a large
number of NOPs followed by his or her code of choice.  This allows
"sledding" into the attackers shellcode.


--
Attack Scenarios:
If a particular service was written using unsafe functions without
bounds checking (strcpy(), strcat(), sprintf() etc...), it is possible
to write arbitrary data to the address space of the service.
Normally, this may just cause the program to die a horrible death.
However, if you can get the return address to point to the beginning
of the newly written data, it is possible to execute code of your
choice.  This requires that the newly written data is actual
executable data.  Since calculating exactly where the return address
may point to is no small task, a popular technique is to pad the space
leading up to your shellcode with NOPs.  This way, if the return
address points anywhere in the series of NOPS, execution will slide
down into your shellcode.

--
Ease of Attack:
Not-so trivial.  This particular technique requires a knowledge of x86
assembly coding, memory, and usually an intimate understanding of the
code that one is attempting to exploit.  Unfortunately, there are
hundreds upon hundreds of canned exploits that nearly anyone with the
ability point-and-click can use and wreak havok with.

--
False Positives:
Many. The x86 NOP can frequently be found in day-to-day traffic,
particularly when transfering large files.

--
False Negatives:
Few.  There are other techniques to emulate a NOP.  Additionally, if
the attackers NOP sled is small enough (< 15), this particular attack
may slip by.  Fortunately, NOP sleds are generally quite large.

--
Corrective Action:
Determine if this NOP was part of an attack or simply part of an
innocent stream of data.

--
Contributors:
Jon Hart <jhart () ccs neu edu>

--
Additional References:
(aleph1's classic article from Phrack?)



At 02:26 PM 4/26/2002 -0500, Taylor Lewick wrote:
> Once I look through a log file and find something I want to investigate 
> more, where do I go to find out more information about what I am seeing, 
> (besides the internet obviously)
>
> For instance, I am seeing a bunch of shellcode x86 NOOP [**] traffic, from 
> one box to another on our network, so I assume nothing too bad is going 
> on.  But how do I find out more about this specific traffic stream, i.e. 
> sid of 648 in shellcodes.rules...  Meaning, if this was a real attack, 
> what kind of attack is it and what kinds of things is it used to do...
>
> Thanks,
> Taylor
>
> Taylor Lewick
> Unix System Administrator
> Fortis Benefits
> 816 881 6073
>
> "Help Wanted.  Seeking Telepath..."
> "You Know where to apply."
>
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