[Snort-users] TCP Portals: The Handshake's a Lie!

Jason Brvenik jasonb at ...1935...
Fri Nov 20 11:12:12 EST 2009

My casual read on it was that you would have to be dealing with a
malicious server which deliberately responds to a syn with a syn and
that the likelihood of that is not the greatest. If it does happen the
server is going to be doing a lot of other more malicious things. My
presumptions are:

- An inbound SYN that is not acknowledging a syn at the same time is
going to be blocked by firewalls if properly configured.

- Even a properly configured border router will be blocking inbound
syn only for non-services ports.

- Any attack relying on local segment access that is a concern means
that you have already failed.

Who would like to provide a server on the net so that people can test
their devices in a full life cycle test? Simple web page returned that
says "It Worked!" would suffice.

On Tue, Nov 17, 2009 at 3:37 PM, Martin Roesch <roesch at ...1935...> wrote:
> On Tue, Nov 17, 2009 at 3:11 PM, CunningPike <cunningpike at ...11827...> wrote:
>> I haven't seen much commentary on this:
>> http://www.breakingpointsystems.com/community/blog/tcp-portals-the-three-way-handshake-is-a-lie.
>> Do any of the snort sigs or preprocessors rely on a SYN/ACK packet for state
>> and/or flow?
> Hi there,
> Stream5 handles the TCP handshaking for the system, I don't think that
> anything else in the codebase cares about the TWH.  I'd have to read the
> code and maybe turn on the debug statements to understand the full effect, I
> know at least some of the state handling handles the SYNs and ACKs
> separately but there could be issues with things like midstream pickups and
> so on.
> Marty
> --
> Martin Roesch - Founder/CTO, Sourcefire Inc. - +1-410-290-1616
> Sourcefire - Security for the Real World - http://www.sourcefire.com
> Snort: Open Source IDP - http://www.snort.org
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