[Oisf-devel] FP on IP frag and sig use udp port 0 ?

[Victor Julien]

On 05/08/2013 12:04 PM, Anoop Saldanha wrote:
> On Wed, May 8, 2013 at 5:27 AM, rmkml <rmkml at yahoo.fr> wrote:
>> Hi,
>>
>> Im curious if anyone confirm this please ?
>> (if yes Im open a new redmine ticket)
>>
>> ok testing Suricata with joigned pcap file contains one IP fragmented packet
>> without UDP layer like this (tshark output):
>>
>> ...
>> Internet Protocol Version 4, Src: 192.168.1.2 (192.168.1.2), Dst:
>> 192.168.1.1 (192.168.1.1)
>>     Version: 4
>>     Header length: 20 bytes
>>     Differentiated Services Field: 0x00
>>         0000 00.. = Default (0x00)
>>         .... ..00 = Not-ECT (Not ECN-Capable Transport) (0x00)
>>     Total Length: 1500
>>     Identification: 0x1061 (4193)
>>     Flags: 0x01 (More Fragments)
>>         0... .... = Reserved bit: Not set
>>         .0.. .... = Don't fragment: Not set
>>         ..1. .... = More fragments: Set
>>     Fragment offset: 1480
>>     Time to live: 64
>>     Protocol: UDP (17)
>>     Header checksum: 0xc0a3 [correct]
>>         [Good: True]
>>         [Bad: False]
>>     Source: 192.168.1.2 (192.168.1.2)
>>     Destination: 192.168.1.1 (192.168.1.1)
>> Data (1480 bytes)
>> 0000  41 41 41 41 41 41 41 41 41 41 41 41 41 41 41 41   AAAAAAAAAAAAAAAA
>> ...
>>
>> Testing with this simply very old sig:
>> alert udp any any <> any 0 (msg:"BAD-TRAFFIC udp port 0 traffic";
>> classtype:misc-activity; sid:525; rev:1;)
>>
>> product Suricata FP alert:
>> 05/06/2013-23:49:28.176296 [**] [1:525:1] BAD-TRAFFIC udp port 0 traffic
>> [**] [Classification: Misc activity] [Priority: 3] {UDP} 192.168.1.2:0 ->
>> 192.168.1.1:0
>>
>> Of course snort not fire.
>>
> 
> Seems right to me.
> 
> We treat it as an ip only sig, the the upper layer protocol is
> determined from the ip packet.
> 

Don't think I agree. The packet is a fragment without the actual UDP
layer. So we have no UDP port info for the packet and thus we can't say
port 0 matched.

-- 
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Victor Julien
http://www.inliniac.net/
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