[Snort-users] file_data entry in snort manual

Bhagya Bantwal bbantwal at ...1935...
Tue Aug 10 10:35:37 EDT 2010

On Mon, Aug 9, 2010 at 11:53 PM, Will Metcalf <william.metcalf at ...11827...>wrote:

> >From the snort manual (note "This option option" typo)....  Hmm I
> think this example is a bit weird, it shows an example that will match
> from the beginning of the payload and is no way relative to setting
> the inspection pointer at the start of file_data so what is the point
> ;-)?

In case of HTTP decompression, file_data will point to the decode buffer
which will have the decompressed data. In this case pcre searches the decode
buffer rather than the packet payload. Hence the example is valid for this
scenario.  But I agree the example suggested is a better one.

> "This option matches if there is HTTP response body or SMTP body. This
> option option will operate similarly to the
> dce stub data option added with DCE/RPC2, in that it simply sets a
> reference for other relative rule options ( byte
> test, byte jump, pcre) to use. This file data can point to either a
> file or a block of data.
Typo will be fixed.


> Example
> alert tcp any any -> any any(msg:"foo at the start of the payload";
> file_data; pcre:"/foo/i";)"
> Perhaps this should be something like....
> alert tcp any 80 -> any any(msg:"foo at the start of http response
> body"; file_data; content:"foo"; nocase; within:3;)
> Regards,
> Will
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