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How to ARPSp00f ? — Part 1

Hi everyone ! I was thinking about doing some tutorials about some basic and important concepts everyone in the h4ck W0r1d should know! So, for this first tutorial, I thought about making a step by step tutorial to learn what is ARP protocol, ARPSpoofing attack and how it works (for learning purpose of course!) Hope you’ll enjoy reading it!

What u should know is that ARP spoofing, also called ARP poisoning, is a very important attack to know because it is used to drive many other attacks! so it is really a MUST to know !

Well first, let me explain to you what is ARP protocol and ARP Spoofing attack in this first part and then we’ll move to some practice in the second part!

ARP’WHAT ?

ARP stands for Address Resolution Protocol, this protocol is used to make the correspondance between an IP address and a MAC address.

OKKK… AND THEN ?

In an Ethernet Network, communication between two or more machines is done at the physical level, every machine is identified uniquely by its MAC address.

Exchanged frames get through the physical layer first, where destination MAC address is checked to accept or not the frame then this one is sent to higher levels if it is accepted, and then IP address is checked at logical level.

There is a correspondence relationship between the physical and the logical addresses of the same machine. Each IP address corresponds to a single MAC address in a LAN. This correspondence is maintained in a table called ARP table or ARP cache in each machine of the network, this table is populated by requests sent via the ARP protocol.

COOOL, BUT how it actually works !?

Well ! when a host wants to communicate with another one on the same LAN knowing its IP address, he needs to get his MAC address (remember : communication in Ethernet Network is done at the physical level, so… We need the MAC address to communicate !)

So first, he will check in his ARP table if there is an entry that corresponds to the IP address of the host with whom he wants to communicate, if yes, then he directly puts the corresponding MAC address in the destination MAC address field of the frame and send it.

However, if the entry is not in its cache, he must send a physical-level broadcast ARP request to all machines in the network so that the one with the corresponding IP address figuring in the destination IP address field of the packet responds with its MAC address in unicast mode to the requester (ARP Reply). After that, a new entry is created in the ARP table of the requester and the frame can finally be sent to the right machine.

OK ! 🤯Now that we finally know what is ARP protocol, then WHAT IS ARP SPOOFING ?

U SPOOF WHAT ? 🙄

What is ARP Spoofing and how it works ?

Well, ARP Spoofing is an attack that exploit ARP protocol, Let’s see how !

This attack exploit a feature in the ARP protocol to spoof the victim ARP table entry corresponding to the IP address we want to spoof!

What u have to know is that an ARP Reply is accepted by a host without any verification, even if he didn’t send an ARP request ! and the ARP table is being updated if the reply is different from the actual entry.

You may ask why ? why accepting a reply without even sending a request ? Well, this is done for performance purposes…!

You got it, right ?

Well, yes … The attacker will simply send crafted packets in huge quantity with a fake MAC address (His MAC Address) corresponding to the spoofed IP at regular intervals of time and the target will update its ARP table and here we go … The victim will communicate with the wrong machine and maybe exchange some sentive data with it ! All the trafic will get through the Attacker machine !

Steps to perform an ARP Spoofing attack

1. Get the IP address of the target (spoofed IP) and the victim : done by scanning passively the network trafic.

2. Building ARP REPLY frames: build ARP responses containing the spoofed IP as IP source and attacker MAC address as source MAC send to the victim in unicast.

3. Sending unsolicited fake ARP REPLY : build ARP reply are sent to the victim in a continuous way at regular time intervals so that the victim will update its ARP table with the fake correspondance.

Here is a simple diagram that summarizes all what have been said before :

ARP Sp00fing Attack example

Hope you enjoyed reading this first part of ARP Spoofing tutorial.

Thanks for reading 😊

PS. Dont forget to send me any suggestion about this article and please let me know about any other solution you propose and don’t forget:

“Knowledge increases by sharing but not by saving.”

― Kamari aka Lyrikal

Enjoy your time being here! 😉

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Amina BALI

Amina BALI

Shellmates Club member, passionate about infosec.

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