Re: How to detect OS with Snort?

[Joel Esler <jesler () sourcefire com>]

On May 8, 2012, at 7:06 PM, Kevin Ross wrote:

> I take it this is due to a policy enforcement in which windows is not allowed? p0f may be a more useful tool to run 
> for this to passively try and fingerprint the OS as it passes. If you are trying to do it via user agent something 
> like this may work:
>
> alert tcp $HOME_NET any -> any any (msg:"WINDOWS User Agent Detected"; flow:established,to_server; content:"Windows"; 
> nocase; http_header; pcre:"/User\x2DAgent\x3A\x20[^\r\n]*Windows/Hi"; classtype:policy-violation; sid:149881; rev:1;)

User Agents can be spoofed.  Easily.  Trivially.


> I don't think snort is the best for this though. If it is actual attacks you are better off looking at detecting 
> attacks from existing sigs that are out there.
>
> If you don't mind me asking so we can understand what you are trying to get to: why is it you want to detect Windows 
> machines on your network? If it is enforcement I would look at making the case for other tools such as packetfence 
> http://www.packetfence.org/home.html but I will try and think of something if you let me know what you hope to 
> achieve with this so I understand what you need to look at.

In OpenSource land, p0f is the best tool to go about detecting OSes.

--
Joel Esler
Senior Research Engineer, VRT
OpenSource Community Manager
Sourcefire


> On 8 May 2012 14:26, Borja Luaces <borja.luaces () gmail com> wrote:
> Good afternoon,
>
> First of all I have to say that I am new to Snort.
>
> I am trying to create an alert rule to detect the OS but everytime I try it it seems not to work.
>
> The rule looks like the following one:
>
> alert tcp any any -> any any (content:"Windows NT";msg:"Microsoft OS detected";)
>
> Any help?
>
> Thanks for your time
>
> -- 
> Borja Luaces Altares
> Administrador/Analista de Sistemas (MCSE Security,C|EH & CSSA)


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