Welcome!

Microsoft Cloud Authors: Elizabeth White, Mihai Corbuleac, Pat Romanski, David Bermingham, Steven Mandel

Related Topics: IoT User Interface, Microsoft Cloud, Cloud Security

IoT User Interface: Tutorial

Intruder Detection with tcpdump

tcpdump tool

To capture, parse, and analyze traffic tcpdump is a very powerful tool. To begin a basic capture uses the following syntax.

tcpdump -n –i <interface> -s <snaplen>

-n      tells tcpdump to not resolve IP addresses to domain names and port numbers to service names.
-I       <interface> tells tcpdump which interface to use.
-s      <snaplen> tells tcpdump how much of the packet to record. I used 1515 but 1514 is sufficient for most cases. If you don’t specify a size then it will only capture the first 68 bytes of each packet. A snaplen value of 0 which will use the required length to catch whole packets can be used except for older versions of tcpdump.

Below is an example output of a dump, although it only contains a few lines it holds much information.

12:24:51.517451  IP  10.10.253.34.2400 > 192.5.5.241.53:  54517 A? www.bluecoast.com.  (34)

12:24:51:517451                              represent the time
10.10.253.34.2400                          Source address and port
>                                                          Traffic direction
192.5.5.241.53                                 Destination address and port
54517                                                 ID number that is shared by both the DNS server 192.5.5.241 and 10.10.253.34
A?                                                        10.10.253.34 asks a question regarding the A record for www.bluecoat.com
(34)                                                     The entire packet is 34 bytes long.

More tcpdump capture options

Here are some examples of options to use when capturing data and why to use them:

-I        specify an interface; this will ensure that you are sniffing where you expect to sniff.
-n       tells tcpdump not to resolve IP addresses to domain names and port numbers to service names
-nn    don’t resolve hostnames or port names
-X      Show packet’s contents in both hex and ASCII
-XX    Include Ethernet header
-v       Increase verbose –vv –vvv more info back
-c       Only get x number of packets and stop
-s       tell tcpdump how much of the packet to record
-S       print absolute sequence numbers
-e       get Ethernet header
-q       show less protocol info
-E       Decrypt IPSEC traffic by providing an encryption key

Packet, Segment, and Datagram
TCP accepts data from a data stream, segments it into chucks, and adds a TCP header creating a TCP segment. UDP sends messages referred to as a datagram to other hosts on an Internet Protocol (IP) network without requiring prior communications to set up special transmission channels or data paths. Internet Protocol then creates its own datagram out of what it receives from TCP or UDP. If the TCP segment or UDP datagram plus IP’s headers are small enough to send in a single package on the wire then IP creates a packet. If they are too large and exceed the maximum transmission unit (MTU) of the media, IP will fragment the datagram into smaller packets suitable to the MTU. The fragmented packets are then reassembled by the destination.

Tcpdump read and write to/from a file
Tcpdump allows you to write data to a file using the –w option and to read from a file with the –r option.

$ sudo tcpdump -i wlan0 -w dumpfile001

$ sudo tcpdump -r dumpfile.pcap

Some people like to see the files as they are captured and have them saved to a file. Use the following options: tcpdump –n –I eth1 –s 1515 –l | tee output.txt
This option tells tcpdump to make its output line-buffered, while piping the output to the tee utility sends output to the screen and the output.txt simultaneously. This command will display packets on the screen while writing data to an output file output.txt it will not be in binary libpcap format. The best way to do this is run a second instance of tcpdump.

Timestamps
When tcpdump captures packets in libpcap format, it adds a timestamp entry to the record in each packet in the capture file. We can augment that data with the –tttt flag, which adds a date to the timestamp (See Figure #1).

Figure 1

You can use the –tt flag to report the number of seconds and microseconds since the UNIX epoch of 00:00:00 UTC on January 1, 1970. If you are not sure you understand the time difference and need to be absolutely sure of time use the –tt option to show seconds and microseconds since the UNIX epoch (See Figure #2).

Figure 2

Useful syntax
Being able to cut the amount of traffic down to just what you are looking for is useful. Here are some useful expressions that can be helpful in tcpdump.

Net – This will capture the traffic on a block of IPs ex 192.168.0.0/24
# tcpdump net 192.168.1.1/24
Src, dst – This will only capture packets form a source or destination.
# tcpdump src 192.168.100.234
# tcpdump dst 10.10.24.56

Host – Capture only traffic based on the IP address
# tcpdump host 10.10.253.34
Proto – Capture works for tcp, udp, and icmp
# tcpdump tcp
Port – Capture packets coming from or going to a port.
# tcpdump port 21
Port ranges – capture packets
# tcpdump port 20-25
Using expressions such as AND [&&], OR [||], & EXCEPT [!]
# tcpdump –n –I eth1 host 10.10.253.34 and host 10.10.33.10
# tcpdump –n –I eht1 src net 10.10.253.0/24 and dst net 10.10.33.0/24 or 192.5.5.241
# tcpdump –n –I eth1 src net 10.10.30.0/24 and not icmp

Searching for info on packets with tcpdump
If you want to search for information in the packet you have to know where to look. Tcpdump starts counting bytes of header information at byte 0 and the 13th byte contains the TCP flags shown in Table #1

<----byte12-----------><--------byte13----------><-----------byte14-----><------byte15------->

Talbe #1

Now looking at byte 13 and if the SYN and ACK are set then your binary value would be 00010010 which are the same as decimal 18. We can search for packets looking for this type of data inside byte 13 shown here.


# tcpdump –n –r dumpfile.lpc –c 10 ‘tcp[13] == 18’ and host 172.16.183.2

Here is a sample of what this command will return shown in Figure #3

Figure #3

When capturing data using tcpdump one way to ignore the arp traffic is to put in a filter like so.


# tcpdump –n –s 1515 –c 5 –I eth1 tcp or udp or icmp

This will catch only tcp, udp, or icmp.

If you want to find all the TCP packets with the SYN ACK flag set or other flags set take a look at Table #2 & tcpdump filter syntax shown below.


flag           Binary           Decimal
URG         00100000          32
ACK          00010000          16
PSH          00001000           8
RST          00000100           4
SYN          00000010           2
FIN            00000001           1
SYNACK  00010010         18

Table #2

Tcpdump filter syntax

Show all URGENT (URG) packets
# tcpdump ‘tcp[13] == 32’
Show all ACKNOWLEDGE (ACK) packets
# tcpdump ‘tcp[13] == 16’
Show all PUSH (PSH) packets
# tcpdump ‘tcp[13] == 8’
Show all RESET (RST) packets
# tcpdump ‘tcp[13] == 4’
Show all SYNCHRONIZE (SYN) packets
# tcpdump ‘tcp[13] ==2’
Show all FINISH (FIN) packets
# tcpdump ‘tcp[13] == 1’
Show all SYNCHRONIZE/ACKNOWLEDGE (SYNACK) packets
# tcpdump ‘tcp[13] == 18’

Using tcpdump in Incident Response

When doing analysis on network traffic using a tool like tcpdump is critical. Below are some examples of using tcpdump to view a couple of different dump files to learn more about network problems or possible attack scenarios. The first is a binary dump file of a snort log and we are given the following information. The IP address of the Linux system is 192.168.100.45 and an attacker got in using a WU-FTPD vulnerability and deployed a backdoor. What can we find out about how the attack happened and what he did?

First we will take a look at the file

# tcpdump –xX –r snort001.log
The log appears long at this point you may want to run the file in snort
# snort –r snort001.log –A full –c /etc/snort/snort.conf
This will give you some info like total packets processed, protocol breakdown, any alerts, etc. See Figure #4 & #5

Figure #4                                                                               Figure #5

Next extract the full snort log file for analysis

# tcpdump –nxX –s 1515 –r snort001.log > tcpdump-full.dat

This will give us a readable file to parse through. After looking through it we find ip-proto-11, which is Network Voice Protocol (NVP) traffic. Now we will search through the file looking for ip-proto-11.


# tcpdump –r snort001.log –w NVP-traffic.log proto 11
This command will read the snort001.log file and look for ‘log proto 11’ and writes the contents to the file NVP-traffic.log. Next we need to be able to view the file because it is a binary file.

# tcpdump –nxX –s 1515 –r NVP-traffic.log > nvp-traffic_log.dat
This will be a file of both hex and ASCII, which is nice but we just want the IP address. Try this.

# tcpdump –r NVP-traffic.log > nvp-traffic_log01.dat
This will give us a list of IP address that were communicating using the Network Voice Protocol (NVP) (See Figure #6).

Figure #6

Next we look at another snort dump file from a compromised windows box that was communicating with an IRC server. What IRC servers did the server at 172.16.134.191 communicate with?

Look for TCP connections originating from the server toward the outside and we can use tcpdump with a filtering expression to capture SYN/ACK packets incoming from outside servers.

# tcpdump -n -nn -r snort_log 'tcp and dst host 172.16.134.191 and tcp[13]==18'

This produces a long list of connections going from 172.16.134.191 to outside connections. (see Figure #7).

Figure #7

Now we know that IRC communicate on port 6666 to 6669 so let’s add that and narrow down the search with the following command.
# tcpdump -n -nn -r snort_log 'tcp and dst host 172.134.16.234 and tcp[13]==18' and portrange 6666-6669 (See output in Figure #8 below)

Figure #8

Now we have narrowed the list down to 3 IP’s that were communicating with the server using IRC.


Tcpdump is a wonderful, general-purpose packet sniffer and incident response tool that should be in your tool shed.

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.

@ThingsExpo Stories
We’ve worked with dozens of early adopters across numerous industries and will debunk common misperceptions, which starts with understanding that many of the connected products we’ll use over the next 5 years are already products, they’re just not yet connected. With an IoT product, time-in-market provides much more essential feedback than ever before. Innovation comes from what you do with the data that the connected product provides in order to enhance the customer experience and optimize busi...
In his session at @ThingsExpo, Chris Klein, CEO and Co-founder of Rachio, will discuss next generation communities that are using IoT to create more sustainable, intelligent communities. One example is Sterling Ranch, a 10,000 home development that – with the help of Siemens – will integrate IoT technology into the community to provide residents with energy and water savings as well as intelligent security. Everything from stop lights to sprinkler systems to building infrastructures will run ef...
Manufacturers are embracing the Industrial Internet the same way consumers are leveraging Fitbits – to improve overall health and wellness. Both can provide consistent measurement, visibility, and suggest performance improvements customized to help reach goals. Fitbit users can view real-time data and make adjustments to increase their activity. In his session at @ThingsExpo, Mark Bernardo Professional Services Leader, Americas, at GE Digital, will discuss how leveraging the Industrial Interne...
The increasing popularity of the Internet of Things necessitates that our physical and cognitive relationship with wearable technology will change rapidly in the near future. This advent means logging has become a thing of the past. Before, it was on us to track our own data, but now that data is automatically available. What does this mean for mHealth and the "connected" body? In her session at @ThingsExpo, Lisa Calkins, CEO and co-founder of Amadeus Consulting, will discuss the impact of wea...
Whether your IoT service is connecting cars, homes, appliances, wearable, cameras or other devices, one question hangs in the balance – how do you actually make money from this service? The ability to turn your IoT service into profit requires the ability to create a monetization strategy that is flexible, scalable and working for you in real-time. It must be a transparent, smoothly implemented strategy that all stakeholders – from customers to the board – will be able to understand and comprehe...
Increasing IoT connectivity is forcing enterprises to find elegant solutions to organize and visualize all incoming data from these connected devices with re-configurable dashboard widgets to effectively allow rapid decision-making for everything from immediate actions in tactical situations to strategic analysis and reporting. In his session at 18th Cloud Expo, Shikhir Singh, Senior Developer Relations Manager at Sencha, will discuss how to create HTML5 dashboards that interact with IoT devic...
Artificial Intelligence has the potential to massively disrupt IoT. In his session at 18th Cloud Expo, AJ Abdallat, CEO of Beyond AI, will discuss what the five main drivers are in Artificial Intelligence that could shape the future of the Internet of Things. AJ Abdallat is CEO of Beyond AI. He has over 20 years of management experience in the fields of artificial intelligence, sensors, instruments, devices and software for telecommunications, life sciences, environmental monitoring, process...
The demand for organizations to expand their infrastructure to multiple IT environments like the cloud, on-premise, mobile, bring your own device (BYOD) and the Internet of Things (IoT) continues to grow. As this hybrid infrastructure increases, the challenge to monitor the security of these systems increases in volume and complexity. In his session at 18th Cloud Expo, Stephen Coty, Chief Security Evangelist at Alert Logic, will show how properly configured and managed security architecture can...
A critical component of any IoT project is the back-end systems that capture data from remote IoT devices and structure it in a way to answer useful questions. Traditional data warehouse and analytical systems are mature technologies that can be used to handle large data sets, but they are not well suited to many IoT-scale products and the need for real-time insights. At Fuze, we have developed a backend platform as part of our mobility-oriented cloud service that uses Big Data-based approache...
SYS-CON Events announced today that Ericsson has been named “Gold Sponsor” of SYS-CON's @ThingsExpo, which will take place on June 7-9, 2016, at the Javits Center in New York, New York. Ericsson is a world leader in the rapidly changing environment of communications technology – providing equipment, software and services to enable transformation through mobility. Some 40 percent of global mobile traffic runs through networks we have supplied. More than 1 billion subscribers around the world re...
SYS-CON Events announced today that Peak 10, Inc., a national IT infrastructure and cloud services provider, will exhibit at SYS-CON's 18th International Cloud Expo®, which will take place on June 7-9, 2016, at the Javits Center in New York City, NY. Peak 10 provides reliable, tailored data center and network services, cloud and managed services. Its solutions are designed to scale and adapt to customers’ changing business needs, enabling them to lower costs, improve performance and focus inter...
The IoTs will challenge the status quo of how IT and development organizations operate. Or will it? Certainly the fog layer of IoT requires special insights about data ontology, security and transactional integrity. But the developmental challenges are the same: People, Process and Platform. In his session at @ThingsExpo, Craig Sproule, CEO of Metavine, will demonstrate how to move beyond today's coding paradigm and share the must-have mindsets for removing complexity from the development proc...
We're entering the post-smartphone era, where wearable gadgets from watches and fitness bands to glasses and health aids will power the next technological revolution. With mass adoption of wearable devices comes a new data ecosystem that must be protected. Wearables open new pathways that facilitate the tracking, sharing and storing of consumers’ personal health, location and daily activity data. Consumers have some idea of the data these devices capture, but most don’t realize how revealing and...
trust and privacy in their ecosystem. Assurance and protection of device identity, secure data encryption and authentication are the key security challenges organizations are trying to address when integrating IoT devices. This holds true for IoT applications in a wide range of industries, for example, healthcare, consumer devices, and manufacturing. In his session at @ThingsExpo, Lancen LaChance, vice president of product management, IoT solutions at GlobalSign, will teach IoT developers how t...
There is an ever-growing explosion of new devices that are connected to the Internet using “cloud” solutions. This rapid growth is creating a massive new demand for efficient access to data. And it’s not just about connecting to that data anymore. This new demand is bringing new issues and challenges and it is important for companies to scale for the coming growth. And with that scaling comes the need for greater security, gathering and data analysis, storage, connectivity and, of course, the...
So, you bought into the current machine learning craze and went on to collect millions/billions of records from this promising new data source. Now, what do you do with them? Too often, the abundance of data quickly turns into an abundance of problems. How do you extract that "magic essence" from your data without falling into the common pitfalls? In her session at @ThingsExpo, Natalia Ponomareva, Software Engineer at Google, will provide tips on how to be successful in large scale machine lear...
Digital payments using wearable devices such as smart watches, fitness trackers, and payment wristbands are an increasing area of focus for industry participants, and consumer acceptance from early trials and deployments has encouraged some of the biggest names in technology and banking to continue their push to drive growth in this nascent market. Wearable payment systems may utilize near field communication (NFC), radio frequency identification (RFID), or quick response (QR) codes and barcodes...
You think you know what’s in your data. But do you? Most organizations are now aware of the business intelligence represented by their data. Data science stands to take this to a level you never thought of – literally. The techniques of data science, when used with the capabilities of Big Data technologies, can make connections you had not yet imagined, helping you discover new insights and ask new questions of your data. In his session at @ThingsExpo, Sarbjit Sarkaria, data science team lead ...
The IETF draft standard for M2M certificates is a security solution specifically designed for the demanding needs of IoT/M2M applications. In his session at @ThingsExpo, Brian Romansky, VP of Strategic Technology at TrustPoint Innovation, will explain how M2M certificates can efficiently enable confidentiality, integrity, and authenticity on highly constrained devices.
You deployed your app with the Bluemix PaaS and it's gaining some serious traction, so it's time to make some tweaks. Did you design your application in a way that it can scale in the cloud? Were you even thinking about the cloud when you built the app? If not, chances are your app is going to break. Check out this webcast to learn various techniques for designing applications that will scale successfully in Bluemix, for the confidence you need to take your apps to the next level and beyond.