file_data pointer

[Eoin Miller <eoin.miller () trojanedbinaries com>]

So if you have a very simple sig that does something like:

aler tcp any $HTTP_PORTS -> any any (msg:"TEST"; file_data;
content:"MZ"; within:2; sid:1;)

I am guessing that file_data's default value is 0, so if the packet
coming into the engine doesn't cause the file_data pointer to have a
value created and the packet does have "MZ" within the first two
bytes, then this will cause an alert to fire. If file_data is not set,
should the rule then not be evaluated on that packet/portion of the
stream? I think that behavior would be quite desirable if you are
trying to fingerprint filetypes more accurately in HTTP protocol streams.

-- Eoin

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