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
"Tintri focuses on the Ops side of the DevOps, which basically is pushing more and more of the accessibility of the infrastructure to the developers and trying to get behind the scenes," explained Dhiraj Sehgal of Tintri in this SYS-CON.tv interview at 20th Cloud Expo, held June 6-8, 2017, at the Javits Center in New York City, NY.
You know you need the cloud, but you’re hesitant to simply dump everything at Amazon since you know that not all workloads are suitable for cloud. You know that you want the kind of ease of use and scalability that you get with public cloud, but your applications are architected in a way that makes the public cloud a non-starter. You’re looking at private cloud solutions based on hyperconverged infrastructure, but you’re concerned with the limits inherent in those technologies.
Cloud applications are seeing a deluge of requests to support the exploding advanced analytics market. “Open analytics” is the emerging strategy to deliver that data through an open data access layer, in the cloud, to be directly consumed by external analytics tools and popular programming languages. An increasing number of data engineers and data scientists use a variety of platforms and advanced analytics languages such as SAS, R, Python and Java, as well as frameworks such as Hadoop and Spark...
The current age of digital transformation means that IT organizations must adapt their toolset to cover all digital experiences, beyond just the end users’. Today’s businesses can no longer focus solely on the digital interactions they manage with employees or customers; they must now contend with non-traditional factors. Whether it's the power of brand to make or break a company, the need to monitor across all locations 24/7, or the ability to proactively resolve issues, companies must adapt to...
Both SaaS vendors and SaaS buyers are going “all-in” to hyperscale IaaS platforms such as AWS, which is disrupting the SaaS value proposition. Why should the enterprise SaaS consumer pay for the SaaS service if their data is resident in adjacent AWS S3 buckets? If both SaaS sellers and buyers are using the same cloud tools, automation and pay-per-transaction model offered by IaaS platforms, then why not host the “shrink-wrapped” software in the customers’ cloud? Further, serverless computing, cl...
You know you need the cloud, but you’re hesitant to simply dump everything at Amazon since you know that not all workloads are suitable for cloud. You know that you want the kind of ease of use and scalability that you get with public cloud, but your applications are architected in a way that makes the public cloud a non-starter. You’re looking at private cloud solutions based on hyperconverged infrastructure, but you’re concerned with the limits inherent in those technologies.
SYS-CON Events announced today that Enzu will exhibit at SYS-CON's 21st Int\ernational Cloud Expo®, which will take place October 31-November 2, 2017, at the Santa Clara Convention Center in Santa Clara, CA. Enzu’s mission is to be the leading provider of enterprise cloud solutions worldwide. Enzu enables online businesses to use its IT infrastructure to their competitive advantage. By offering a suite of proven hosting and management services, Enzu wants companies to focus on the core of their ...
With major technology companies and startups seriously embracing Cloud strategies, now is the perfect time to attend 21st Cloud Expo October 31 - November 2, 2017, at the Santa Clara Convention Center, CA, and June 12-14, 2018, at the Javits Center in New York City, NY, and learn what is going on, contribute to the discussions, and ensure that your enterprise is on the right path to Digital Transformation.
In his session at @ThingsExpo, Eric Lachapelle, CEO of the Professional Evaluation and Certification Board (PECB), provided an overview of various initiatives to certify the security of connected devices and future trends in ensuring public trust of IoT. Eric Lachapelle is the Chief Executive Officer of the Professional Evaluation and Certification Board (PECB), an international certification body. His role is to help companies and individuals to achieve professional, accredited and worldwide re...
In the world of DevOps there are ‘known good practices’ – aka ‘patterns’ – and ‘known bad practices’ – aka ‘anti-patterns.' Many of these patterns and anti-patterns have been developed from real world experience, especially by the early adopters of DevOps theory; but many are more feasible in theory than in practice, especially for more recent entrants to the DevOps scene. In this power panel at @DevOpsSummit at 18th Cloud Expo, moderated by DevOps Conference Chair Andi Mann, panelists discussed...
Wooed by the promise of faster innovation, lower TCO, and greater agility, businesses of every shape and size have embraced the cloud at every layer of the IT stack – from apps to file sharing to infrastructure. The typical organization currently uses more than a dozen sanctioned cloud apps and will shift more than half of all workloads to the cloud by 2018. Such cloud investments have delivered measurable benefits. But they’ve also resulted in some unintended side-effects: complexity and risk. ...
With the introduction of IoT and Smart Living in every aspect of our lives, one question has become relevant: What are the security implications? To answer this, first we have to look and explore the security models of the technologies that IoT is founded upon. In his session at @ThingsExpo, Nevi Kaja, a Research Engineer at Ford Motor Company, discussed some of the security challenges of the IoT infrastructure and related how these aspects impact Smart Living. The material was delivered interac...
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...
IoT solutions exploit operational data generated by Internet-connected smart “things” for the purpose of gaining operational insight and producing “better outcomes” (for example, create new business models, eliminate unscheduled maintenance, etc.). The explosive proliferation of IoT solutions will result in an exponential growth in the volume of IoT data, precipitating significant Information Governance issues: who owns the IoT data, what are the rights/duties of IoT solutions adopters towards t...
Today we can collect lots and lots of performance data. We build beautiful dashboards and even have fancy query languages to access and transform the data. Still performance data is a secret language only a couple of people understand. The more business becomes digital the more stakeholders are interested in this data including how it relates to business. Some of these people have never used a monitoring tool before. They have a question on their mind like “How is my application doing” but no id...