Building a Cat-5 Cable Tap

by Ashes

This article is a tutorial on how to build a special Category 5 cable to physically tap into an existing Cat 5 cable.

The idea came to me on a deployment in Iraq when our Tactical Operations Center (TOC) had numerous Cat 5 cables that were exposed (the TOC was manned 24x7).  I thought how easy it would be in a corporate environment to connect a physical tap to one of these wires, most commonly found in drop ceilings.

The first step to making this tap cable is to cut one of the ends.  If creating from a reel of cable, leave one of the ends exposed and terminate the other end with an RJ45 connector.  The next step is to strip the outer coating and each individual wire, exposing the metal wire.

Next, you need to solder the bare metal wires to alligator clips.  In the images below, I soldered and taped the ends for a stronger hold.

Now that your cable is built, it is ready to attack (or test, depending on your hat color).

To begin the attack, you need to strip the victim's Cat 5 cable (all individual wires) down to the metal without cutting it.  Tricky - it takes patience and finesse.  After the metal of all the wires has been exposed, you can connect the attacking cable's alligator clips to the victim's exposed metal wires.

Important:  When connecting the alligator clips, you must match the colors from the attacker's cable to the colors of the victim's cable.  For example, blue-white on attacker cable needs to attach to blue-white on victim cable, etc.

Make sure that the alligator clips do not touch.

In the below pictures, I used parts of the outer shell of the victim's Cat 5 cable to keep the clips separated.  If the alligator clips touch, the connection will drop.

Once your attacking machine is connected to the Cat 5 tap cable, fire up the packet sniffer, go to promiscuous mode, and sniff away!

    

    

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This design may have impedance issues, add series 1 kΩ resistors if it effects the network.