Welcome!

Cloud Security Authors: Elizabeth White, Pat Romanski, Maria C. Horton, Liz McMillan, Ravi Rajamiyer

Related Topics: Cloud Security, Industrial IoT, Microservices Expo, Adobe Flex, Agile Computing

Cloud Security: Article

Capture File Filtering with Wireshark

Needle in a Haystack

Intrusion detection tools that use the libpcap C/ C++ library [1] for network traffic capture (such as Snort [2] and Tcpdump [1]) can output packet capture information to a file for later reference. The format of this capture file is known as pcap. By capturing packet data to a file, an investigator can return later to study the history of an intrusion attempt – or to turn up other important clues about clandestine activity on the network.

Of course, the traffic history data stored in a pcap file is much too vast to study by just viewing the file manually. Security experts use specialized filtering tools to search through the file for pertinent information. One way to look for clues in a pcap file is to use the Wireshark protocol analysis tool [3] and its accompanying command-line utility tshark.

Wireshark is included by default on many Linux distros, and if not, it is available through the leading package repositories. You can also download Wireshark through the project website [4]. In this article, I describe how to use Wireshark and tshark to search a pcap file for information on network activity. I will assume you already have a pcap file ready for investigation. For more on how to capture a pcap file with Tcp-dump, see my article “Intruder Detection with Tcpdump,” which is available online at the ADMIN magazine website [5].

tshark at the Command Line
The tshark utility is a simple tool included with the Wireshark package that lets you filter the contents of a pcap file from the command line. To get a view of the most significant activity, I use the following command:

$ tshark ‑nr dumpfile1.gz ‑qz "io,phs" > details.txt

The ‑n switch disables network object name resolution, ‑r indicates that packet data is to be read from the input file, in this case dumpfile1.gz. The ‑z allows for statistics to display after it finishes reading the capture file, the ‑q flag specifies that only the statistics are printed, and the > redirection
sends the output to the file called details.txt. See Figure 1 for the output of this information. To view a list of help commands used with tshark, type:

$ tshark ‑h

And for a list of ‑z arguments type:

$ tshark ‑z help

Figure 1

Say you would like to know whether a particular IP address appeared in a packet dump and what port it was connecting on. The following command line checks the dump file for the IP address 98.139.126.21:

$ tshark ‑V ‑nr dumpfile.gz ip.src == 98.139.126.21 | grep "Source port" | awk {'print $3'} | sort ‑n | uniq 80

The resulting output on the line following the command shows that the packet dump file recorded IP address 98.139.126.21 having connections on port 80.

If you were given a packet dump file and asked to find possible IRC traffic on your network, how would you do it? First, you would need to know what port numbers were associated with IRC traffic, and that could be accomplished with Google or by issuing the following command:

$ grep irc /usr/share/nmap/nmap‑services | grep tcp

Figure 2 shows the results of the preceding command.

Figure 2

Now I can search the packet dump and look for evidence of IRC traffic using the following commands:

$ tshark ‑nr dumpfile1.gz 'ip.addr==172.16.134.191 and tcp.port >=  6667 and tcp.port <= 6670 and irc' |  awk {'print $3,$4,$5,$6'} | sort ‑n | uniq ‑c

Figure 1: tshark statistics output.
Figure 2: Locating IRC port numbers with grep.
Figure 3: IRC connections found in the packet dump.
Figure 4: The Wireshark startup window.

The breakdown of this command is shown in Table 1, and the output is in Figure 3.

Figure 3

In the GUI
The Wireshark GUI application is easier on the eyes, and it provides some options that aren’t available at the command line. You can start Wireshark from the Application menu or from the terminal.  To load a capture file, select Open in the startup window (Figure 4) or select File | Open from the menubar.  Once you have a packet capture file loaded, you can start searching packet dumps within the Wireshark interface.

Figure 4

The Filter box below the Wireshark toolbar lets you enter criteria for the search. For instance, to search for all the Canonical Name records within the capture file, type in the following filter: dns.resp.type == CNAME (see Figure 5).  After you enter a filter, remember to clear the filter text to see the full file before starting a new search.

Figure 5

Table 1: Parts of a tshark Command

Option Description
‘ip.addr==172.16.134.191         This is my network
and tcp.port >= 6667                   Start of the port range
and tcp.port <= 6670                   End of the port range
and irc’                                           Searches for IRC traffic only
awk {‘print $3,$4,$5,$6’}             Prints the third through sixth patterns from each matching line
sort ‑n                                            Sorts according to string numerical value
uniq ‑c                                            Only prints the number of matches that are unique

Digging deeper, if I want to know how long a client resolver cached the IP address associated with the name cookex.amp.gapx.yahoodns.net (Figure 6), I would enter the following filter:

dns.resp.name == "cookex.amp.gapx. yahoodns.net"

Figure 6

The filter ip.addr == 10.37.32.97 gives information on all communications that involve 10.37.32.97 in the packet dump. If needed, use && to isolate to a specific protocol. The filter ip.dst == 10.37.32.97 or ip.src == 10.37.32.97 looks for a source or destination IP address.

How could I find the password used over Telnet between two IP addresses? For example, if a user at 172.21.12.5 is using Telnet to access a device at 10. 37. 140.160, I can enter:

ip.dst == 10.37.140.160 && ip.src == 172.21.12.5 && telnet.data contains "Password"

The preceding command will list the connections that meet the search requirement, and you can right-click on the packet and click Follow TCP Stream to view the password. (See Figures 7 and 8.)

Figure 7

Figure 8

Note: A much easier way to get the password on the network, if you were sniffing the traffic instead of reading from a capture file, would be to use ettercap, as follows:

$ ettercap ‑Tzq //23

To discover whether someone was viewing a suspicious web page, I can perform a filter search to find out what picture the person at IP address 10.225.5.107 was viewing at Yahoo (216.115.97.236) with the following filter:

ip.dst == 10.225.5.107 && ip.src == 216.115.97.236 && (image‑jfif || image‑gif)

Figure 9

Figure 9 shows the results. If you then right-click on a line in the output and select Follow TCP Stream for the results shown in Figure 10.
The second line in the Follow TCP Stream output specifies that wynn‑ rovepolitico.jpg is the image this person was viewing on the site.

Figure 10

Conclusion
Wireshark can do more than just watch the wires in real time. If you save a snapshot of network activity in a capture file in the pcap format, you can use Wireshark to search through the file to look for clues about nefarious activity.

In this article, I described how to search for information in a capture file using Wireshark and the tshark command-line tool.

Info

[1] Tcpdump and Libpcap: http://www.tcpdump.org/
[2] Snort: http://www..snort.org
[3] Wireshark: http://www.wireshark.org/
[4] Wireshark Download: http://www.wireshark.org/download.html
[5] “Intruder Detection with Tcpdump” by David J. Dodd: http://www.admin‑magazine.com/Articles/Intruder‑Detection‑with‑tcpdump/

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.

IoT & Smart Cities Stories
The platform combines the strengths of Singtel's extensive, intelligent network capabilities with Microsoft's cloud expertise to create a unique solution that sets new standards for IoT applications," said Mr Diomedes Kastanis, Head of IoT at Singtel. "Our solution provides speed, transparency and flexibility, paving the way for a more pervasive use of IoT to accelerate enterprises' digitalisation efforts. AI-powered intelligent connectivity over Microsoft Azure will be the fastest connected pat...
There are many examples of disruption in consumer space – Uber disrupting the cab industry, Airbnb disrupting the hospitality industry and so on; but have you wondered who is disrupting support and operations? AISERA helps make businesses and customers successful by offering consumer-like user experience for support and operations. We have built the world’s first AI-driven IT / HR / Cloud / Customer Support and Operations solution.
Codete accelerates their clients growth through technological expertise and experience. Codite team works with organizations to meet the challenges that digitalization presents. Their clients include digital start-ups as well as established enterprises in the IT industry. To stay competitive in a highly innovative IT industry, strong R&D departments and bold spin-off initiatives is a must. Codete Data Science and Software Architects teams help corporate clients to stay up to date with the mod...
At CloudEXPO Silicon Valley, June 24-26, 2019, Digital Transformation (DX) is a major focus with expanded DevOpsSUMMIT and FinTechEXPO programs within the DXWorldEXPO agenda. Successful transformation requires a laser focus on being data-driven and on using all the tools available that enable transformation if they plan to survive over the long term. A total of 88% of Fortune 500 companies from a generation ago are now out of business. Only 12% still survive. Similar percentages are found throug...
Druva is the global leader in Cloud Data Protection and Management, delivering the industry's first data management-as-a-service solution that aggregates data from endpoints, servers and cloud applications and leverages the public cloud to offer a single pane of glass to enable data protection, governance and intelligence-dramatically increasing the availability and visibility of business critical information, while reducing the risk, cost and complexity of managing and protecting it. Druva's...
BMC has unmatched experience in IT management, supporting 92 of the Forbes Global 100, and earning recognition as an ITSM Gartner Magic Quadrant Leader for five years running. Our solutions offer speed, agility, and efficiency to tackle business challenges in the areas of service management, automation, operations, and the mainframe.
The Jevons Paradox suggests that when technological advances increase efficiency of a resource, it results in an overall increase in consumption. Writing on the increased use of coal as a result of technological improvements, 19th-century economist William Stanley Jevons found that these improvements led to the development of new ways to utilize coal. In his session at 19th Cloud Expo, Mark Thiele, Chief Strategy Officer for Apcera, compared the Jevons Paradox to modern-day enterprise IT, examin...
With 10 simultaneous tracks, keynotes, general sessions and targeted breakout classes, @CloudEXPO and DXWorldEXPO are two of the most important technology events of the year. Since its launch over eight years ago, @CloudEXPO and DXWorldEXPO have presented a rock star faculty as well as showcased hundreds of sponsors and exhibitors! In this blog post, we provide 7 tips on how, as part of our world-class faculty, you can deliver one of the most popular sessions at our events. But before reading...
DSR is a supplier of project management, consultancy services and IT solutions that increase effectiveness of a company's operations in the production sector. The company combines in-depth knowledge of international companies with expert knowledge utilising IT tools that support manufacturing and distribution processes. DSR ensures optimization and integration of internal processes which is necessary for companies to grow rapidly. The rapid growth is possible thanks, to specialized services an...
At CloudEXPO Silicon Valley, June 24-26, 2019, Digital Transformation (DX) is a major focus with expanded DevOpsSUMMIT and FinTechEXPO programs within the DXWorldEXPO agenda. Successful transformation requires a laser focus on being data-driven and on using all the tools available that enable transformation if they plan to survive over the long term. A total of 88% of Fortune 500 companies from a generation ago are now out of business. Only 12% still survive. Similar percentages are found throug...