Thread: Address Resolution Protocol (ARP) Attacks

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What Does ARP Mean?
Address Resolution Protocol (ARP) is a stateless protocol, was designed to map Internet Protocol addresses (IP) to their associated Media Access Control (MAC) addresses. This being said, by mapping a 32 bit IP address to an associated 48 bit MAC address via attached Ethernet devices, a communication between local nodes can be made.

On a majority of operating systems, such as Linux, FreeBSD, and other UNIX based operating systems, and even including Windows, the "arp" program is present. This program can be used to display and/or modify ARP cache entries.

An example of the "arp" utility's output would look like the following:

Windows:
> arp -a
Interface: 192.168.1.100 .- 0x10003
Internet Address Physical Address Type
192.168.1.1 00-13-10-23-9a-53 dynamic

Linux:
$ arp -na
? (192.168.1.1) at 00:90:B1C:F8:C0 [ether] on eth0

FreeBSD:
$ arp -na
? (192.168.1.1) at 00:00:0c:3e:4d:49 on bge0

How ARP works?
Specifically for Internet Protocol Version 4 (IPv4), ARP maps IP addresses between the Network layer and Data Link layer of the Open System Interconnection (OSI) model.
For a more complete and thorough explanation of how address resolution works, and protocol specifics, please consult RFC 826.

ARP Protocol Flaws
ARP's main flaw is in its cache. Knowing that it is possible for ARP to update existing entries as well as add to the cache, this leads one to believe that forged replies can be made, which result in ARP cache poisoning attacks.

Some terms:
ARP Cache Poisoning : Broadcasting forged ARP replies on a local network. In a sense, "fooling" nodes on the network. This can be done because ARP lacks authentication features, thus blindly accepting any request and reply that is received or sent.

MAC Address Flooding : An ARP cache poisoning attack that is mainly used in switched environments. By flooding a switch with fake MAC addresses, a switch is overloaded. Because of this, it broadcasts all network traffic to every connected node. This outcome is referred to as "broadcast mode" because, all traffic passing through the switch is broadcasted out like a Hub would do. This then can result in sniffing all network traffic.

# Connection Hijacking & Interception : Packet or connection hijacking and interception is the act in which any connected client can be victimized into getting their connection manipulated in a way that it is possible to take complete control over.

# Connection Resetting : The name explains itself very well. When we are resetting a client's connection, we are cutting their connection to the system. This can be easily done using specially crafted code to do so. Luckily, we have wonderful software that was made to aid us in doing so.

# Man In The Middle : One of the more prominent ways of attacking another user in order to hijack their traffic, is by means of a Man In The Middle (MITM) attack. Unlike the other attacks, a MITM is more a packet manipulation attack which in the end however does result in packet redirection to the attacker . all traffic will get sent to the attacker doing the MITM attack. This attack however is specific. As opposed to MAC Address Flooding or other attacks against a router/switch, the MITM attack is against a victim, and also can be done outside of a switched environment. Thus meaning, an attack can be executed against a person on the other side of the count

# Packet Sniffing : Sniffing on a Local Area Network (LAN) is quite easy if the network is segmented via a hub, rather than a switch. It is of course possible to sniff on a switched environment by performing a MAC flood attack. As a result of the MAC flood, the switch will act as a hub, and allow the entire network to be sniffed. This gives you a chance to use any sort of sniffing software available to you to use against the network, and gather packets.

# Denial of Service : MAC Address Flooding can be considered a Denial of service attack. The main idea of the MAC flood, is to generate enough packet data to send toward a switch, attempting to make it panic. This will cause the switch to drop into broadcast mode and broadcast all packet data. This however did not result in a crash, or the service to be dropped, but to be overloaded.