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

[Anoop Saldanha]

On Tue, May 21, 2013 at 2:01 PM, Victor Julien <victor at inliniac.net> wrote:
> 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.
>

Right.  I overlooked the port part.

-- 
Anoop Saldanha