[Snort-sigs] Snort not inspecting all traffic sourcing from itself?

L0rd Ch0de1m0rt l0rdch0de1m0rt at ...2420...
Wed Jun 9 16:45:45 EDT 2010


Hello.  I'm curious.  I am running Snort 2.8.5.1 on an Ubuntu 8.04
web server and I have the following two very simple rules enabled (and
nothing else):

alert tcp any any -> any any (msg:"TCP SYN packet seen!"; flags:S;
classtype:bad-unknown; sid:54002346; rev:1;)

alert tcp any any -> any any (msg:"HTTP GET detected"; content:"GET";
nocase; classtype:bad-unknown; sid:68000036; rev:1;)

Now before people start complaining, this is for testing only, not
real rules so no need to criticise them.  Anyway if I make a HTTP GET
request from a different machine to the Snort machine (which is
running a web server, remember), both rules fire.  If the Snort
machine serves up a web page that has the word "GET" in it, the rules
fire again (different HTTP session).  However, if I log on to the
Snort machine, fire up a web browser, and start surfing, only the SYN
rule fires despite the fact that "GET" is clearly in traffic when I do
a tcpdump on it.  So for some reason, Snort is not inspecting all
traffic (although some since the SYN rule fired) sourcing from itself.
 Here are my Streams5 options in snort.conf:

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, small_segments 3 bytes 150, timeout 180, \
    ports client 21 22 23 25 42 53 79 109 110 111 113 119 135 136 137 139 143 \
        161 445 513 514 587 593 691 1433 1521 2100 3306 6665 6666 6667
6668 6669 \
        7000 32770 32771 32772 32773 32774 32775 32776 32777 32778 32779, \
    ports both 80 443 465 563 636 989 992 993 994 995 1220 2301 3128
6907 7702 7777 7779 7801 7900 7901 7902 7903 7904 7905 \
        7906 7908 7909 7910 7911 7912 7913 7914 7915 7916 7917 7918
7919 7920 8000 8008 8028 8080 8180 8888 9999
preprocessor stream5_udp: timeout 180

Cheers,

-L0rd Ch0de1m0rt




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