JSI Tip 7836. FPipe.exe freeware TCP/IP and UDP source port forwarder/redirector.

Download Fpipe2_1.zip.

The FPipe readme file contains:

 ------------------------------------------------------------------------------FPipe v2.1 - Port redirector.Copyright 2000 (c) by Foundstone, Inc.http://www.foundstone.com------------------------------------------------------------------------------FPipe is a source port forwarder/redirector. It can create a TCP or UDP streamwith a source port of your choice. This is useful for getting past firewallsthat allow traffic with source ports of say 23, to connect with internalservers.Usually a client has a random, high numbered source port, which the firewallpicks off in its filter. However, the firewall might let Telnet trafficthrough. FPipe can force the stream to always use a specific source port, inthis case the Telnet source port. By doing this, the firewall 'sees' thestream as an allowed service and let's the stream through.FPipe basically works by indirection. Start FPipe with a listening serverport, a remote destination port (the port you are trying to reach insidethe firewall) and the (optional) local source port number you want. WhenFPipe starts it will wait for a client to connect on its listening port.When a listening connection is made a new connection to the destinationmachine and port with the specified local source port will be made - creatingthe needed stream. When the full connection has been established, FPipeforwards all the data received on its inbound connection to the remotedestination port beyond the firewall.FPipe can run on the local host of the application that you are trying to useto 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 compromisedwith MDAC. A netcat shell is waiting on that HTTP server, but you can'ttelnet because the firewall blocks it off. Start FPipe with the destinationof the netcat listener, a listening port and a source port that the firewallwill let through. Telnet to FPipe and you will be forwarded to the NetCatshell. 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 specifyan outbound connection source port number and the outbound connection becomesclosed, they MAY not be able to re-establish a connection to the remotemachine (FPipe will claim that the address is already in use) until theTCP TIME_WAIT and CLOSE_WAIT periods have elapsed. This time period can rangeanywhere from 30 seconds to 4 minutes or more depending on which OS andversion you are using. This timeout is a feature of the TCP protocol and isnot a limitation of FPipe itself.The reason this occurs is because FPipe tries to establish a new connectionto the remote machine using the same local IP/port and remote IP/portcombination as in the previous session and the new connection cannot be madeuntil the TCP stack has decided that the previous connection has completelyfinished up.------------------------------------------------------------------------------Connection illustration-----------------------The connection terminology used in the program and in the followingdocumentation 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 v2.1 - TCP/UDP port redirector.Copyright 2000 (c) by Foundstone, Inc.http://www.foundstone.comFPipe [-hvu?] [-lrs ] [-i IP] IP -?/-h - shows this help text -c    - maximum allowed simultaneous TCP connections. Default is 32 -i    - listening interface IP address -l    - listening port number -r    - remote port number -s    - outbound source port number -u    - UDP mode -v    - verbose modeDetailed option descriptions-----------------------------h or -?Shows the usage of the program as in the above text.-cSpecifies the maximum number of simultaneous TCP connections that the programcan handle. The default number is 32. If you are planning on using FPipefor forwarding HTTP requests it might be advisable to raise this number.-iSpecifies the IP interface that the program will listen on. If this option isnot used FPipe will listen on whatever interface the operating systemdetermines is most suitable.-lSpecifies the FPipe listening server port number. This is the port numberthat listens for connections on the FPipe machine.-rSpecifies the remote port number. This is the port number on the remotemachine that will be connected to.-sSpecifies the outbound connection local source port number. This is theport number that data sent from the FPipe server machine will come fromwhen sent to the remote machine.-uSets the program to run in UDP mode. FPipe will forward all UDP data sentto and received from either side of the FPipe server (the machine on whichFPipe is running). Since UDP is a connectionless protocol the -c option ismeaningless with this option.-vVerbose mode. Additional information will be shown if you set the programto verbose mode.IPSpecifies the remote host IP address.------------------------------------------------------------------------------To best illustrate the use of FPipe here is an example.Example #1:fpipe -l 53 -s 53 -r 80 192.168.1.101This would set the program to listen for connections on port 53 andwhen a local connection is detected a further connection will bemade to port 80 of the remote machine at 192.168.1.101 with thesource port for that outbound connection being set to 53 also.Data sent to and from the connected machines will be passed through.==============================================================================FOUNDSTONE, INC.Terms of Use1. Acceptance of Terms1.1.Read these Foundstone, Inc. 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