Re: Deny IP spoof from 255.255.255.255

["Crist Clark" <crist.clark () globalstar com>]

Vitaly Osipov wrote:
> this is a sample of your packet:
>
> #(1 - 29543) [2001-06-19 01:34:54] [arachNIDS/203]  BACKDOOR Q access
> IPv4: 255.255.255.255 -> x.x.x.x
>       hlen=5 TOS=0 dlen=43 ID=0 flags=0 offset=0 TTL=13 chksum=45614
> TCP:  port=31337 -> dport: 515  flags=***A*R** seq=0
>       ack=0 off=5 res=0 win=0 urp=0 chksum=25942
> Payload:  length = 3
>
> 000 : 63 6B 6F                                          cko

Yeah, those are the RST ones. They crack me up even more than the
more common SYN ones. In order for the RST ones to do anything, 
the victim must not only respond to a packet with the broadcast
address as the source, but it would have to respond to a RST which
any sane TCP implementation will never, ever, ever do.

I see a lot more of the SYN ones. They look like,

  17:22:40.938837 255.255.255.255.31337 > AAA.BBB.CC4.192.515: S 100:100(0) win 512 (ttl 242, id 62128)
  03:16:51.069740 255.255.255.255.31337 > AAA.BBB.CC5.161.515: S 100:100(0) win 512 (ttl 242, id 62128)

Note the TCP sequence number and IP ID. They are always the same. (These 
two just happen to have the same TTL, but I get a distribution).
-- 
Crist J. Clark                                Network Security Engineer
crist.clark () globalstar com                    Globalstar, L.P.
(408) 933-4387                                FAX: (408) 933-4926

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