Re: All tcp ports open?
From: Chris Brenton (cbrenton_at_chrisbrenton.org)
Date: 08/30/04
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To: Ben Timby <asp@webexc.com> Date: Mon, 30 Aug 2004 06:37:59 -0400
On Sun, 2004-08-29 at 03:04, Ben Timby wrote:
>
> 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.
Been there seen this, its how I like to configure a perimeter. ;-)
A number of firewalls will do this if you tweak them right. Gauntlet,
iptables, 4.x and prior Firewall-1, and TCPWrapper just to name a few.
You can also see this type of response out of load balancers and SYN
flood protection devices.
> I can connect via netcat any of the ports, and
> send data, but nothing is returned.
So you complete a TCP three packet handshake, send a single ACK with a
payload, and _nothing_ comes back, not even a RST? If so I would lean
more towards it being a firewall giving you this response.
> In order to verify services, I am
> required to connect and check for a banner or send appropriate protocol
> commands to elicit a response.
nmap is your friend:
nmap -sT -P0 -A -O -F -oN scan.txt 1.1.1.1/24
"-A" will do some app specific queries to see if there is actually
anything listening on the port.
I included "-O" because if all the IP's fingerprint exactly the same,
its very likely you are talking to a firewall. It sounded like you might
be checking only 1 IP address however, in which case you can't compare
the fingerprints of different IPs. You can however at least check to see
if the fingerprint is for a known firewall that displays the activity
you describe.
I included "-F" so you are not scanning *every* port. On the up side
your scan will go quicker. On the downside, you'll miss apps on
non-standard ports.
Happy fishing!
Chris
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