From: Tim (tim-pentest@sentinelchicken.org)
Date: Sun Aug 29 2004 - 13:42:45 EDT
> I am not sure what is doing this, but I assume it is a software (or some
> kind of) firewall/hids, can anybody point me in the right direction?
>
> I am pen-testing a Windows webserver, and a port scan reveals ALL tcp
> ports open. hping also confirms that a SA is returned for any S packets
> sent to any port I try. I can connect via netcat any of the ports, and
> send data, but nothing is returned. In order to verify services, I am
> required to connect and check for a banner or send appropriate protocol
> commands to elicit a response.
>
> Has anyone seen this, or have any idea of what this is?
I have seen some load balancers behave this way, but it could also be a
firewall responding with SYN/ACK on blocked ports to make it harder for
an attacker to see what is open. (The book "Hacking: The Art of
Exploitation" by Jon Erickson describes a strategy like this, though I
am sure there are many other papers that do as well.) Are you scanning
with a SYN scan, or a full connect()? When you connect to a port that
you are pretty sure should be closed, does the host ACK your data that
you send once the connection is established? If not, then it is
probably just a sneaky FW configuration.
Have you tried other scans (FIN, ACK, Xmas, etc)?
tim
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