Re: snort rule

[rmkml <rmkml () free fr>]

Hi lokesh,
maybe good starting with this :
  alert udp any any -> any 67 (msg:"DHCP Service byte-code sequence exploit detected"; content:"|01 48 23 87 AB 1F FA 
2C 9A 00 00 00 00 21 FF FF|"; classtype:shellcode-detect; sid:999999; rev:1;)
Finding your byte-code sequence on dhcp request is easy (byte-code sequence is long and reduce FP), and finding invalid 
input HLen on dhcp request is very hard.
Best Regards
Rmkml


On Wed, 29 Aug 2007, lokesh sharma wrote:

> Date: Wed, 29 Aug 2007 18:42:55 +1000 (EST)
> From: lokesh sharma <lokeshpunjabi_1984 () yahoo com au>
> To: Snort-users () lists sourceforge net
> Subject: [Snort-users] snort rule
>
> can you help me
>  to write rules regarding DHCP
>  The rule is
>  "detect all attempts to exploit this vulnerability. In particular, it should detect attempts by any computer making 
> DHCP requests where hte Hlen
>  field has an invalid value, and where the following byte-code sequence is found anywhere in the Sname or File fields.
>  The byte-code sequence should not be matched in any other field of the request. The byte-code sequence (in 
> hexadecimal) is:
>  01 48 23 87 AB 1F FA 2C 9A 00 00 00 00 21 FF FF
>   on detecction of such attack attempts, your rule should generate an alert with the message:
>  "DHCP Service invalid input HLen attack detected".
>
>  thanx
>
>
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