[Snort-sigs] Question about Content-Disposition, Content-Type, etc. and http_header buffer

Joel Esler jesler at ...435...
Tue Oct 16 17:51:50 EDT 2012


Can you send me a pcap?

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

On Oct 16, 2012, at 5:18 PM, Mike Cox <mike.cox52 at ...2420...> wrote:

> I've noticed that in some multipart/form-data POSTs, data that is normally in the HTTP header gets sent in the body of the message and not parsed by http-inspect as part of the http_header buffer.  Specifically, the headers "Content-Type", "Content-Disposition", and "Content-Transfer-Encoding", although there could be others.  For example:
> 
> POST /blackhole/safe.php HTTP/1.1
> Host: snort.org
> Content-Type: multipart/form-data, boundary=---dG91Y2hteXNub3J0
> Content-Length: 8675309
> 
> ---dG91Y2hteXNub3J0
> Content-Disposition: form-data; name="name"
> 
> Joshua
> ---dG91Y2hteXNub3J0
> Content-Disposition: form-data; name="play_a_game"
> 
> True
> ---dG91Y2hteXNub3J0
> Content-Disposition: form-data; name="file"; filename="GLOBAL_THERMONUCLEAR_WAR.pdf"
> Content-Type: application/pdf
> Content-Transfer-Encoding: binary
> ...
> 
> So a snort rule looking for a specific filename in a Content-Disposition header wouldn't match if it were written as you would expect it to be written.  For example, this wouldn't match the above:
> 
> alert tcp $HOME_NET any -> $EXTERNAL_NET $HTTP_PORTS (msg:"Bad PDF File Upload"; flow:established,to_server; content:"Content-Disposition"; http_header; content:"filename="; distance:0; http_header; content:".pdf"; distance:0; within:100; http_header; sid:1234567;)
> 
> What is the best way to match this and not incur the overhead of using global content matches?  Is there a plan for the http-inspect pre-processor to account for this?
> 
> Thanks.
> 
> -Mike Cox
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