Re: BAD TRAFFIC data in TCP SYN packet

[Laurie Zirkle <lat () cns vt edu>]

Here's the explanation I received last year when pursuing this further:

"This system is a 3DNS box from F5. It performs data center load
balancing by trying to determine which data center you are closest to
and routes you there. It does this through some pretty strange and
intrusive ways and it looks like this box was not brought up in one of
the approved configurations. Pounding port 53 is one of the intrusive
things the product is know to do. I've passed it on to the folks who
created that approved configuration and police the misconfigured boxes."

Of course, it took repeated messages and finally blocking them to
get this to stop.  And this was the only "real" message about this
whole mess I got back from them.  I saw this on one of our nameservers
from Sep 22 20:33:37 -> Oct  2 05:32:19 and on another one from
Oct 24 08:02:57 -> Nov  4 21:53:26.  And I noticed over this past
weekend that it's started again to yet another of our nameservers.

--
Laurie

> From the fingers of Martin Roesch:
> Generally speaking, you're not supposed to send application data in the
> SYN packet (it's bad form to send application layer data before the
> connection is even established), that's what this alert is firing on. 
> It's probably just a bad stack implementation.
>
>      -Marty
>
> Matt Kettler wrote:
> > Well, the port 29291 is just a random local port.. This is a syn packet
> > remember, so the service being used is on destination end, and is port 53
> > (dns).
> >
> > so, 207.46.106.84 has decided that 172.40.20.235 might be a dns server, and
> > has attempted to connect to it via TCP (it is unusual, but legal for a DNS
> > server to be contacted via tcp instead of UDP).
> >
> > I've seen some similar traffic myself from a pair of DNS servers directed
> > at the local DNS server here.. the TCP syn packets contain several bytes of
> > data which are all 00's. It is strange (AFAIK it is not legal to send data
> > with a syn packet.. you haven't negotiated a connection yet), but it
> > appears to be an artifact of a buggy tcp/ip implementation.. Or who knows,
> > it may be an artifact of some obscure, buggy worm  or scanning tool that
> > looks at DNS servers and uses raw sockets instead of the local TCP/IP
> > stack. Even if it is from some obscure hacking tool, the syn packets
> > themselves appear harmless.
> >
> > At 07:39 AM 1/14/2002 +0100, you wrote:
> > > Hi!
> > >
> > > I get a lot of
> > >
> > > 01/14-02:24:17.089098  [**] [1:526:3] BAD TRAFFIC data in TCP SYN packet
> > > [**] [Classification: Misc activity] [Priority: 3] {TCP} 207.46.106.84:29291
> > > -> 172.40.20.235:53
> > >
> > > 172.40.20.235 is my DNS server, but why would clients put data in the syn
> > > packets? According to RIPE, the source address is "ALLOCATED UNSPECIFIED",
> > > so I can't find out who's doing this. It comes from a limited number of
> > > addresses, they all seem to be 207.xx.xxx.xxx.

-- 
Laurie

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