[Snort-sigs] Snort 2.8.6 and gzip decoding functionality not working for me

Bhagya Bantwal bbantwal at ...435...
Tue May 4 16:18:38 EDT 2010


Turning on stream reassembly might be useful too.

Do you have a pcap we could look into?


-B

On Tue, May 4, 2010 at 3:40 PM, L0rd Ch0de1m0rt <l0rdch0de1m0rt at ...2420...>wrote:

> Hello.  I am experimenting with snort v2.8.6 and hope to benefit from
> its gzip decoding capabilities.  However, I have been unsuccessful so
> far in getting it to work.  I am fetching a javascript file from
> google and clearly it is encoding it using gzip.  This rule alerts me:
>
> alert tcp any any -> any any (msg:"gzip encoding detected from
> server"; flow:established,from_server; content:"|0d
> 0a|Content-Encoding: gzip|0d 0a|"; nocase; classtype:attempted-user;
> sid:3141591; rev:1;)
>
> BUT this rule does not alert when it is clearly in the gzip decoded data:
>
> alert tcp any any -> any any (msg:"detected on gzip decoded data from
> Google"; flow:established,from_server; content:"google.isOpera=false";
> nocase; classtype:attempted-user; sid:3141592; rev:1;)
>
> I am using the defaults for the gzip portion of the http_inspect
> preprocessor and the content trying to be matched
> (google.isOpera=false) is in the first few hundred bytes of the data.
> Here is my snort.conf http_inspect details:
>
> preprocessor http_inspect: global iis_unicode_map unicode.map 1252
> preprocessor http_inspect_server: server default \
>   apache_whitespace no \
>   ascii no \
>        bare_byte no \
>        chunk_length 500000 \
>   server_flow_depth 0 \
>   client_flow_depth 0 \
>   post_depth 65495 \
>        directory no \
>        double_decode no \
>        iis_backslash no \
>        iis_delimiter no \
>        iis_unicode no \
>        multi_slash no \
>        non_strict \
>        oversize_dir_length 500 \
>        ports { 80 1220 2301 3128 7777 7779 8000 8008 8028 8080 8180
> 8888 9999 } \
>        u_encode yes \
>        non_rfc_char { 0x00 0x01 0x02 0x03 0x04 0x05 0x06 0x07 } \
>        webroot no \
>        extended_response_inspection \
>        inspect_gzip
>
> I configured snort with --enable-zlib before I compiled and I get this
> on snort startup:
>
> Using ZLIB version: 1.2.3.3
>
> What am I doing wrong here?  Thanks for any help.
>
> Cheers,
>
> -L0rd Ch0de1m0rt
>
>
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