[Snort-sigs] new rule for detect windows NAT DNS DoS

Blake Hartstein bhartstein at ...274...
Tue Oct 31 11:01:26 EST 2006


My data shows this also valid over tcp.
This rule is too generic, I tested it with a large amount of DNS traffic 
and legitimate requests cause false positives very frequently, namely:

The header field "Questions" has a value of 00 01
And the data following contains multiple null bytes.

Is there a better way to anchor this detection?

-Blake


rmkml wrote:
> Hi,
>
> please check and maybe add this new rule :
>
> dns.rules:alert udp $EXTERNAL_NET any -> $HOME_NET 53 (msg:"DNS Windows 
> NAT DoS attempt"; content:"|01 00|"; offset:2; content:"|00 00|"; 
> offset:10; reference:cve,2006-5614; classtype:bad-unknown; rev:1;)
>
> "Overview: Microsoft Windows NAT Helper components (ipnathlp.dll) on 
> windows XP SP2, when internet connection sharing is enabled, allows remote 
> attackers to cause DoS (svchost.exe crash) via malformed DNS query, which 
> results in a null pointer dereference."
>
> Any suggestions and improvements are welcome,
>
> This rule is offered by Crusoe Researches (Team)
> http://www.crusoe-researches.com
>
> Regards
> Rmkml
>
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