Related Topics: Cloud Security, Mobile IoT

Cloud Security: Article

Network Security: Arp Cache Poisoning and Sniffing Packets

ARP Cache Poisoning allows any computer on the local area network to obtain one of the most powerful attack postures in network

In a switched network environment packets are sent to their destination port by MAC address. This requires that hardware be able to create and maintain a table associating MAC addresses to ports. In a switched environment packets are only sent to devices that they are meant for. Even in this switched environment there are ways to sniff other devices' packets. One such way is to spoof your MAC address and poison the arp table. Since there is no state information about ARP traffic kept, as it's a simple protocol, the arp cache can be overwritten (unless the entry was explicitly marked as permanent).

Arp cache poisoning puts the attacker in position to intercept communications between the two computers. Computer A believes it is communicating with Computer B, but because of the poisoned arp table, the communication actually goes to the attacker's computer. The attacker can then either respond to computer A (pretending to be computer B), or simply forward the packets to its intended destination, but only after the packet information is captured and logged for later sue by the attacker. Likewise, the response from Computer B can be captured and logged by the attacker, who has also used Arp poisoning to make Computer B think its Computer A. this type of attack is known as Man in the Middle attack.

This article will cover a number of tools used in arp cache poisoning including ettercap, arpspoof, nemesis, p0f, dsniff, and scapy.

Running Ettercap
For arp cache poisoning to take place the attacker needs to be in the same network segment as the systems that are to communicate between each other. The first step is to obtain a list of IP addresses and the associated MAC. This can be accomplished a couple of different ways, one with a tool called ettercap. Ettercap is a suite for man in the middle attacks on your local LAN. It features sniffing of live connections, content filtering on the fly and more. It supports active and passive dissection of many protocols some of them we will cover in this paper.

# ettercap -T -M arp:remote //

This command will quickly sniff all hosts within your subnet, to view the results type L or hit h for the help menu and you will be given a list of commands.

Arp Cache DOS
To arp poison a given IP address to knock them off line so they cant communicate with anyone use arpspoof from the dsniff suite. Arpspoof is much simpler than ettercap to redirect packets, here is an example:

# arpspoof -i eth0 -t <target> host

Specifying the interface is optional but required if more than one interface is present. The -t specifies the particular host to ARP poison and if not specified all hosts on the LAN will be poisoned. The host can be the default gateway and this will keep the target from communicating beyond the local segment. Arpspoof redirects packets from a target host or all hosts on the LAN intended for another host on the LAN by forging ARP replies. The beauty of this program comes from the arp_send() function, which also uses libnet to spoof packets. The arp_send() sends out one ARP packet with source/target IP and Ethernet hardware addresses supplied by the user. Libnet is a generic networking API that provides access to several protocols.

To better understand how this works lets look at another tool called nemesis. If we have the IP and MAC of the intended target and host we can use nemesis to arp poison our target and leave them with a denial of service. Nemesis is a command-line network packet crafting and injection utility. Nemesis can craft and inject ARP, DNS, ETHERNET, ICMP, IGMP, IP, OSPF, RIP, TCP and UDP packets. By crafting your own packet using nemesis you can see how the arp cache poisoning works.

$ sudo nemesis arp -v -r -d eth0 -S -D -h 00:22:6E:71:04:BB -m 00:0C:29:B2:78:9E -H 00:22:6E:71:04:BB -M 00:0C:29:B2:78:9E

Then we create a packet to send in the other direction.

$ sudo nemesis arp -v -r -d eth0 -S -D -h 00:22:6E:71:04:BB -m 00:22:6B:7E:AD:7C -H 00:22:6E:71:04:BB -M 00:22:6B:7E:AD:7C

These two commands spoof ARP replies from to then from to The nemesis arp options -S specifies the source IP address, -D the destination IP address, -h the senders MAC address, -m the target MAC address, -H the source MAC address, and -M the destination MAC address. These two commands send bogus ARP replies to keep the ARP caches poisoned and traffic redirected. I find understanding this aspect allows you a better understanding of how the arp cache poisoning works. Lets replay them every 10 seconds with a loop.

$ while true

> do

> sudo nemesis arp -v -r -d eth0 -S -D -h 00:22:6E:71:04:BB -m 00:0C:29:B2:78:9E -H 00:22:6E:71:04:BB -M 00:0C:29:B2:78:9E

> sudo nemesis arp -v -r -d eth0 -S -D -h 00:22:6E:71:04:BB -m 00:22:6B:7E:AD:7C -H 00:22:6E:71:04:BB -M 00:22:6B:7E:AD:7C

> echo "Redirecting"

> sleep 10

> done

Once this is done the targeted box will be off-line and unable to communicate with the rest of the network. I made a video on my site that demonstrates this attack and is available at http://pbnetworks.net.

Sniffing the LAN
The bridge mode in ettercap requires two interfaces that are placed in the network segment. If you setup in-line with network bridge mode you are very hard to detect. In bridge mode you intercept packets and can read, sniff, or change them before sending them on to the victim. This mode is stealthy because you don't send out ARP packets on the LAN.

# ettercap -Tq -i eth0 -B eth1

The -i sets the primary interface as eth0, the -B sets the second bridging interface (see Figure #1).

If you run in GTK+ user interface you can do this by Sniff => Bridged sniffing

Figure 1: Sniffing traffic

Logging data
If you would like to log all the packets in a file you can use a number of different tools such as p0f which is a versatile passive OS fingerprinting and masquerade detection utility. It can be used for evidence or information gathering on servers, firewalls, and intrusion detection systems. Ettercap can also fingerprint hosts (find the Operating System running) with the -P option, just need to specify an open port. Once we find out what Operating system we are dealing with then it we can anticipate how the system will react.

# ettercap -Tq -P finger /

To allow the p0f utility to write packets to tcpdump snapshot use the -w option.

p0f -w dumpfile.pcap

dsniff has a collection of tools used for network penetration testing and audits. These tools include dsniff, filesnarf, mailsnarf, nsgsnarf, urlsnard, and webspy passively monitor a network for interesting data. Arpspoof, dnsspoof, and macof tools facilitate the interception of network traffic normally unavailable to an attacker due to layer-2 switching. Below we are using the -w option to to write packets to file.

dsniff -w dumpfile.pcap

Ettercap allows dumping packet data to file with the -w option as well.

ettercap -T -M arp:remote / / -w dumpfile.pcap

It is easier and less intrusive if you specify a specific box to sniff traffic and write to a file then trying to sniff the whole LAN segment. Otherwise you may crash ettercap. You can then view the output in Scapy if you have a graphical PostScript/PDF. Scapy is a powerful interactive packet manipulation program that has the ability to forge or decode packets of a wide number of protocols. It can perform tasks like scanning, tracerouting, probing, unit tests, network discovery, tcpdump, tethereal, p0f and much more. Start by typing scapy at the terminal prompt.

$ scapy

>>> a=rdpcap("/home/cr0wn/dumpfile.pcap")

>>> a

<dumpfile.pcap: TCP:9522 UDP:2386 IMCP:15 Other:611>

>>> a[423].pdfdump(layer_shift=1)

See Figure 2

Figure 2 Scapy graphical output

A good way to protect yourself while you are web-browsing is to use HTTP Everywhere by the Electronic Frontier Foundation (EFF). This will allow https to be used instead of http which passes information in clear-text and would be read by an attacker that is sniffing the local network segment. This is becomes more significant when using unknown wireless networks like at coffee shops or airports.

Sniffing with Scapy
The ability to capture packets and clone tcpdump is possible with scapy. Here we find a host that we want to sniff traffic on and use this command:

>>> sniff(filter="tcp and hsot", count=50)

>>> a=_

>>> a.nsummary()

Here we are sniffing the next 50 packets traveling the network on the host

(see Figure 3).

Figure 3 sniffing 50 packets

If we use the sprintf() function we can get even more control over what is displayed.

>>> pkts = sniff(prn=lambda x:x.sprintf("{IP:%IP.src% → %IP.dst%\n}{Raw:%Raw.load%\n}"))

(see Figure 4).

Figure #4 different control displays in scapy

If we use the sprintf() function we can get even more control over what is displayed.

>>> pkts = sniff(prn=lambda x:x.sprintf("{IP:%IP.src% → %IP.dst%\n}{Raw:%Raw.load%\n}"))

see Figure #4).

We can narrow down the ports that we sniff on such as port 25 and 110, common ports for mail client. Enter the following command in scapy:

>>> a=sniff(filter="tcp and ( port 25 or port 110 )",

prn=lambda x: x.sprintf(%IP.src%:TCP.sport% → %IP.dst%:%TCP.dport% %2s,TCP.flags% : %TCP.payload%"))

In the above we are sniffing for tcp on ports 25 and 110 and using the lambda operator, used to denote anonymous functions, with the sprintf() function for more control over displayed information.

The above can be viewed in Figure 5.

Figure 5 sniffing user names and passwords using Scapy

Scapy can also graph what you are sniffing on the network by producing a simple diagram of packet flow. The conversations() method will create a conversation graph which requires graphviz and ImageMagick to work. Here I am using scapy to sniff the wireless interface (wlan0) that is connected to a foreign network, all displayed in a graphic format.

>>> a=sniff(iface="wlan0", prn=lambda x: x.summary())

>>> a.conversations()

The output above can be seen in Figure 6.

Figure 6 graphical output with Scapy

ARP Cache Poisoning allows any computer on the local area network to obtain one of the most powerful attack postures in network security called "Man in the Middle" (MITM). MITM is able to monitor, filter, modify and edit any and all network traffic moving between LANs. In this article we have identified some open source tools that can be used to launch attacks on switched networks. We have identified some easy ways to prevent data loss by using a browser add-on. By making yourself aware and familiar with some of these tools you can see how secure your network really is. A good solution is to provide port security integrated into your switches and by running arpwatch to monitor address resolution protocol traffic on your network.

This article appears in Admin Network & Security Magazine on-line edition.  They had a difficult time getting all the .jpgs to work with their web application so I am publishing the article here as well.

Let pbnetworks get your pen test on target

Visit us and learn how http://pbnetworks.net

How secure is your network?

More Stories By David Dodd

David J. Dodd is currently in the United States and holds a current 'Top Secret' DoD Clearance and is available for consulting on various Information Assurance projects. A former U.S. Marine with Avionics background in Electronic Countermeasures Systems. David has given talks at the San Diego Regional Security Conference and SDISSA, is a member of InfraGard, and contributes to Secure our eCity http://securingourecity.org. He works for Xerox as Information Security Officer City of San Diego & pbnetworks Inc. http://pbnetworks.net a Service Disabled Veteran Owned Small Business (SDVOSB) located in San Diego, CA and can be contacted by emailing: dave at pbnetworks.net.

Latest Stories
Enterprises have taken advantage of IoT to achieve important revenue and cost advantages. What is less apparent is how incumbent enterprises operating at scale have, following success with IoT, built analytic, operations management and software development capabilities – ranging from autonomous vehicles to manageable robotics installations. They have embraced these capabilities as if they were Silicon Valley startups. As a result, many firms employ new business models that place enormous impor...
SYS-CON Events announced today that TidalScale will exhibit at SYS-CON's 21st International Cloud Expo®, which will take place on Oct 31 – Nov 2, 2017, at the Santa Clara Convention Center in Santa Clara, CA. TidalScale is the leading provider of Software-Defined Servers that bring flexibility to modern data centers by right-sizing servers on the fly to fit any data set or workload. TidalScale’s award-winning inverse hypervisor technology combines multiple commodity servers (including their ass...
As popularity of the smart home is growing and continues to go mainstream, technological factors play a greater role. The IoT protocol houses the interoperability battery consumption, security, and configuration of a smart home device, and it can be difficult for companies to choose the right kind for their product. For both DIY and professionally installed smart homes, developers need to consider each of these elements for their product to be successful in the market and current smart homes.
SYS-CON Events announced today that MIRAI Inc. will exhibit at the Japan External Trade Organization (JETRO) Pavilion at SYS-CON's 21st International Cloud Expo®, which will take place on Oct 31 – Nov 2, 2017, at the Santa Clara Convention Center in Santa Clara, CA. MIRAI Inc. are IT consultants from the public sector whose mission is to solve social issues by technology and innovation and to create a meaningful future for people.
In his general session at 21st Cloud Expo, Greg Dumas, Calligo’s Vice President and G.M. of US operations, will go over the new Global Data Protection Regulation and how Calligo can help business stay compliant in digitally globalized world. Greg Dumas is Calligo's Vice President and G.M. of US operations. Calligo is an established service provider that provides an innovative platform for trusted cloud solutions. Calligo’s customers are typically most concerned about GDPR compliance, applicatio...
Companies are harnessing data in ways we once associated with science fiction. Analysts have access to a plethora of visualization and reporting tools, but considering the vast amount of data businesses collect and limitations of CPUs, end users are forced to design their structures and systems with limitations. Until now. As the cloud toolkit to analyze data has evolved, GPUs have stepped in to massively parallel SQL, visualization and machine learning.
In his Opening Keynote at 21st Cloud Expo, John Considine, General Manager of IBM Cloud Infrastructure, will lead you through the exciting evolution of the cloud. He'll look at this major disruption from the perspective of technology, business models, and what this means for enterprises of all sizes. John Considine is General Manager of Cloud Infrastructure Services at IBM. In that role he is responsible for leading IBM’s public cloud infrastructure including strategy, development, and offering ...
As hybrid cloud becomes the de-facto standard mode of operation for most enterprises, new challenges arise on how to efficiently and economically share data across environments. In his session at 21st Cloud Expo, Dr. Allon Cohen, VP of Product at Elastifile, will explore new techniques and best practices that help enterprise IT benefit from the advantages of hybrid cloud environments by enabling data availability for both legacy enterprise and cloud-native mission critical applications. By rev...
SYS-CON Events announced today that Dasher Technologies will exhibit at SYS-CON's 21st International Cloud Expo®, which will take place on Oct 31 - Nov 2, 2017, at the Santa Clara Convention Center in Santa Clara, CA. Dasher Technologies, Inc. ® is a premier IT solution provider that delivers expert technical resources along with trusted account executives to architect and deliver complete IT solutions and services to help our clients execute their goals, plans and objectives. Since 1999, we'v...
SYS-CON Events announced today that NetApp has been named “Bronze Sponsor” of SYS-CON's 21st International Cloud Expo®, which will take place on Oct 31 – Nov 2, 2017, at the Santa Clara Convention Center in Santa Clara, CA. NetApp is the data authority for hybrid cloud. NetApp provides a full range of hybrid cloud data services that simplify management of applications and data across cloud and on-premises environments to accelerate digital transformation. Together with their partners, NetApp emp...
SYS-CON Events announced today that TidalScale, a leading provider of systems and services, will exhibit at SYS-CON's 21st International Cloud Expo®, which will take place on Oct 31 - Nov 2, 2017, at the Santa Clara Convention Center in Santa Clara, CA. TidalScale has been involved in shaping the computing landscape. They've designed, developed and deployed some of the most important and successful systems and services in the history of the computing industry - internet, Ethernet, operating s...
Join IBM November 1 at 21st Cloud Expo at the Santa Clara Convention Center in Santa Clara, CA, and learn how IBM Watson can bring cognitive services and AI to intelligent, unmanned systems. Cognitive analysis impacts today’s systems with unparalleled ability that were previously available only to manned, back-end operations. Thanks to cloud processing, IBM Watson can bring cognitive services and AI to intelligent, unmanned systems. Imagine a robot vacuum that becomes your personal assistant tha...
SYS-CON Events announced today that Massive Networks, that helps your business operate seamlessly with fast, reliable, and secure internet and network solutions, has been named "Exhibitor" of SYS-CON's 21st International Cloud Expo ®, which will take place on Oct 31 - Nov 2, 2017, at the Santa Clara Convention Center in Santa Clara, CA. As a premier telecommunications provider, Massive Networks is headquartered out of Louisville, Colorado. With years of experience under their belt, their team of...
Widespread fragmentation is stalling the growth of the IIoT and making it difficult for partners to work together. The number of software platforms, apps, hardware and connectivity standards is creating paralysis among businesses that are afraid of being locked into a solution. EdgeX Foundry is unifying the community around a common IoT edge framework and an ecosystem of interoperable components.
In his session at 21st Cloud Expo, Michael Burley, a Senior Business Development Executive in IT Services at NetApp, will describe how NetApp designed a three-year program of work to migrate 25PB of a major telco's enterprise data to a new STaaS platform, and then secured a long-term contract to manage and operate the platform. This significant program blended the best of NetApp’s solutions and services capabilities to enable this telco’s successful adoption of private cloud storage and launchi...