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

L0rd Ch0de1m0rt l0rdch0de1m0rt at ...2420...
Tue May 4 16:31:36 EDT 2010


Matts, thanks for the responses.  Using the config options that
Watchinski provided yielded the same results as initially described.
Bhagya, I think I have streams enabled; please correct me if I am
wrong:

# cat /etc/snort/snort.conf | grep -i -A 10 stream
# Target-Based stateful inspection/stream reassembly.  For more
inforation, see README.stream5
preprocessor stream5_global: max_tcp 8192, track_tcp yes, track_udp
yes, track_icmp no
preprocessor stream5_tcp: policy windows, detect_anomalies, require_3whs 180, \
   overlap_limit 10, check_session_hijacking, small_segments 3 bytes
150, timeout 180, \
   ports client 21 22 23 25 42 53 79 80 109 110 111 113 119 135 136
137 139 143 110 \
      111 161 445 513 514 691 1220 1433 1521 2100 2301 3128 3306 6665
6666 6667 6668 6669 \
      7000 8000 8080 8180 8888 32770 32771 32772 32773 32774 32775
32776 32777 32778 32779, \
   ports both 443 465 563 636 989 992 993 994 995 7801 7702 7900 7901
7902 7903 7904 7905 \
      7906 6907 7908 7909 7910 7911 7912 7913 7914 7915 7916 7917 7918 7919 7920
preprocessor stream5_udp: timeout 180

# performance statistics.  For more information, see the Snort Manual,
Configuring Snort - Preprocessors - Performance Monitor
# preprocessor perfmonitor: time 300 file /var/snort/snort.stats pktcnt 10000

# HTTP normalization and anomaly detection.  For more information, see
README.http_inspect
# preprocessor http_inspect: global iis_unicode_map unicode.map 1252
preprocessor http_inspect: global iis_unicode_map unicode.map 1252
compress_depth 20480 decompress_depth 20480
preprocessor http_inspect_server: server default \
   apache_whitespace no \
   ascii no \

As for pcaps, yes they can be provided but I have looked in to them
myself and have confirmed the behaviour described.  I am concerned
about anonamyzing them since the google javascript data may contain
PII in the URI and/or cookies.  Do you know of a good site that uses
gzip without PII that I can use to test and give you pcaps?

Thanks again.

Cheers,

-L0rd Ch0de1m0rt

On Tue, May 4, 2010 at 3:18 PM, Bhagya Bantwal <bbantwal at ...435...> wrote:
> 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 ...3420....>
> 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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>




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