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FPipe_2.01

FPipe_2.01
Posted Aug 22, 2000
Authored by Foundstone Labs | Site foundstone.com

FPipe is a TCP source port forwarder/redirector that can be used to force a TCP stream to always connect using a specific source port. This tool can be used to get around firewalls that only accept traffic originating from common source ports.

tags | tcp
SHA-256 | f9c86a366b0ceda5db685b75cbef40028ce0b3a845d63910cbbe40da1d0a0ec8

FPipe_2.01

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============================================================================
==
Tool: FPIPE v2.01
Author: Foundstone, Inc.
Platform: NT, 2000
Description: FPipe is a TCP source port forwarder/redirector. It can create
a TCP stream with a source port of your choice. This is useful for getting
past firewalls that allow traffic with source ports of say 23, to connect
with internal servers.

For more info contact labs@foundstone.com

============================================================================
==

README.TXT:

----------------------------------------------------------------------------
--
FPipe v2.01 - Port redirector.
Copyright 2000 (c) by Foundstone, Inc.
http://www.foundstone.com
----------------------------------------------------------------------------
--

FPipe is a TCP source port forwarder/redirector. It can create a TCP stream
with a source port of your choice. This is useful for getting past firewalls
that allow traffic with source ports of say 23, to connect with internal
servers.

Usually a client has a random, high numbered source port, which the firewall
picks off in its filter. However, the firewall might let Telnet traffic
through. FPipe can force the stream to always use a specific source port, in
this case the Telnet source port. By doing this, the firewall 'sees' the
stream as an allowed service and let's the stream through.

FPipe basically works by indirection. Start FPipe with a listening server
port, a remote destination port (the port you are trying to reach inside
the firewall) and the (optional) local source port number you want. When
FPipe starts it will wait for a client to connect on its listening port.
When a listening connection is made a new connection to the destination
machine and port with the specified local source port will be made -
creating
the needed stream. When the full connection has been established, FPipe
forwards all the data received on its inbound connection to the remote
destination port beyond the firewall.

FPipe can run on the local host of the application that you are trying to
use
to get inside the firewall, or it can listen on a 3rd server somewhere else.

Say you want to telnet to an internal HTTP server that you just compromised
with MDAC. A netcat shell is waiting on that HTTP server, but you can't
telnet because the firewall blocks it off. Start FPipe with the destination
of the netcat listener, a listening port and a source port that the firewall
will let through. Telnet to FPipe and you will be forwarded to the NetCat
shell. Telnet and FPipe can exist on the same server, or on different
servers.

----------------------------------------------------------------------------
--

*** IMPORTANT ***

Users should be aware of the fact that if they use the -s option to specify
an outbound connection source port number and the outbound connection
becomes
closed, they MAY not be able to re-establish a connection to the remote
machine (FPipe will claim that the address is already in use) until the
TCP TIME_WAIT and CLOSE_WAIT periods have elapsed. This time period can
range
anywhere from 30 seconds to 4 minutes or more depending on which OS and
version you are using. This timeout is a feature of the TCP protocol and is
not a limitation of FPipe itself.

The reason this occurs is because FPipe tries to establish a new connection
to the remote machine using the same local IP/port and remote IP/port
combination as in the previous session and the new connection cannot be made
until the TCP stack has decided that the previous connection has completely
finished up.

----------------------------------------------------------------------------
--

Connection illustration
-----------------------

The connection terminology used in the program and in the following
documentation can be shown in the form of the following diagram.


Local Machine <----------> FPipe server <---------> Remote machine
Inbound Outbound
connection connection

----------------------------------------------------------------------------
--

This is the usage line as reported by typing "FPipe", "FPipe -h" or
"FPipe -?".

FPipe v2.01 - TCP port redirector.
Copyright 2000 (c) by Foundstone, Inc.
http://www.foundstone.com

FPipe [-hv?] [-brs <port>] IP

-?/-h - shows this help text
-l - listening port number
-r - remote TCP port number
-s - outbound connection source port number
-v - verbose mode


Detailed option descriptions
----------------------------

-h or -?
Shows the usage of the program as in the above text.

-l
Specifies the FPipe listening server port number. This is the port number
that listens for connections on the FPipe machine.

-r
Specifies the remote port number. This is the port number on the remote
machine that will be connected to.

-s
Specifies the outbound connection local source port number. This is the
port number that data sent from the FPipe server machine will come from
when sent to the remote machine.

-v
Verbose mode. Additional information will be shown if you set the program
to verbose mode.

IP
Specifies the remote host IP address.

----------------------------------------------------------------------------
--


To best illustrate the use of FPipe here is an example.


Example #1:
fpipe -l 53 -s 53 -r 80 192.168.1.101

This would set the program to listen for connections on port 53 and
when a local connection is detected a further connection will be
made to port 80 of the remote machine at 192.168.1.101 with the
source port for that outbound connection being set to 53 also.
Data sent to and from the connected machines will be passed through.


============================================================================
==
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