[Snort-users] stream4_reassembly problems

Eric J. Bowser ebowser at ...13800...
Wed May 3 12:32:04 EDT 2006


Hi All,

It seems like stream4 reassembly is quite often lumping packets together
unnecessarily.  I'm running snort 2.4.3 with mySQL support compiled in and
the SPADE patch, on RedHat 9.0.

For example, here is a packet dump, captured by a rule from bleeding edge,
"MALWARE Fun Web Products Spyware User Agent (1)"  I have clipped the data
to only show the user agent portions, and prevent revealing anything private.

Based on the contents, it seems there are three separate GET requests here,
to three different sites, from three different web browsers on three
different machines.

Why are these lumped together into a single packet and passed to snort for
scanning?  The IP address reported by snort in the packet headers is not
event the infected machine!  The entire packet logged by snort is 1875 bytes
long by the way...

This is happening on several rules, and is even causing false positives
because of multiple packets being lumped together.

Thanks for any direction you can provide...

...
030 : 6F 6F 67 6C 65 2E 63 6F 6D 0D 0A 55 73 65 72 2D   oogle.com..User-
040 : 41 67 65 6E 74 3A 20 4D 6F 7A 69 6C 6C 61 2F 35   Agent: Mozilla/5
050 : 2E 30 20 28 57 69 6E 64 6F 77 73 3B 20 55 3B 20   .0 (Windows; U;
060 : 57 69 6E 64 6F 77 73 20 4E 54 20 35 2E 31 3B 20   Windows NT 5.1;
070 : 65 6E 2D 55 53 3B 20 72 76 3A 31 2E 38 2E 30 2E   en-US; rv:1.8.0.
080 : 32 3B 20 47 6F 6F 67 6C 65 2D 54 52 2D 31 29 20   2; Google-TR-1)
090 : 47 65 63 6B 6F 2F 32 30 30 36 30 33 30 38 20 46   Gecko/20060308 F
0a0 : 69 72 65 66 6F 78 2F 31 2E 35 2E 30 2E 32 0D 0A   irefox/1.5.0.2..
...
440 : 3A 32 34 61 22 0D 0A 55 73 65 72 2D 41 67 65 6E   :24a"..User-Agen
450 : 74 3A 20 4D 6F 7A 69 6C 6C 61 2F 34 2E 30 20 28   t: Mozilla/4.0 (
460 : 63 6F 6D 70 61 74 69 62 6C 65 3B 20 4D 53 49 45   compatible; MSIE
470 : 20 36 2E 30 3B 20 57 69 6E 64 6F 77 73 20 4E 54    6.0; Windows NT
480 : 20 35 2E 31 3B 20 53 56 31 3B 20 46 75 6E 57 65    5.1; SV1; FunWe
490 : 62 50 72 6F 64 75 63 74 73 3B 20 2E 4E 45 54 20   bProducts; .NET
4a0 : 43 4C 52 20 31 2E 31 2E 34 33 32 32 29 0D 0A 48   CLR 1.1.4322)..H
4b0 : 6F 73 74 3A 20 69 6D 61 67 65 73 32 2E 73 69 6E   ost: images2.sin
...
610 : 65 0D 0A 55 73 65 72 2D 41 67 65 6E 74 3A 20 4D   e..User-Agent: M
620 : 6F 7A 69 6C 6C 61 2F 34 2E 30 20 28 63 6F 6D 70   ozilla/4.0 (comp
630 : 61 74 69 62 6C 65 3B 20 4D 53 49 45 20 36 2E 30   atible; MSIE 6.0
640 : 3B 20 57 69 6E 64 6F 77 73 20 4E 54 20 35 2E 31   ; Windows NT 5.1
650 : 3B 20 53 56 31 3B 20 2E 4E 45 54 20 43 4C 52 20   ; SV1; .NET CLR
660 : 31 2E 31 2E 34 33 32 32 3B 20 49 6E 66 6F 50 61   1.1.4322; InfoPa
670 : 74 68 2E 31 29 0D 0A 48 6F 73 74 3A 20 63 6F 6E   th.1)..Host: con

-- 
Eric J. Bowser
Bright.Net NE / Doylestown Communications, Inc.
800-535-6423 toll-free
www.neobright.net
www.doyestowncommunications.com

¨Providing advanced communications since 1899.¨

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