Network%20Forensics

1
Case study Ann

• Section 3.1
• Network Forensics
• TRACKING HACKERS THROUGH CYBERSPACE

2
Scenario Anns Bad AIM

• Anarchy-R-Us, Inc. suspects that one of their
  employees, Ann Dercover, is really a secret agent
  working for their competitor. Ann has access to
  the companys prize asset, the secret recipe.
  Security staff are worried that Ann may try to
  leak the companys secret recipe.
• Security staff have been monitoring Anns
  activity for some time, but havent found
  anything suspicious until now. Today an
  unexpected laptop briefly appeared on the company
  wireless network. Staff hypothesize it may have
  been someone in the parking lot, because no
  strangers were seen in the building. Anns
  computer, (192.168.1.158) sent IMs over the
  wireless network to this computer. The rogue
  laptop disappeared shortly thereafter.
• We have a packet capture of the activity, said
  security staff, but we cant figure out whats
  going on. Can you help?
• http//forensicscontest.com/2009/09/25/puzzle-1-an
  ns-bad-aim

3
Mission

• You are the forensic investigator. Your mission
  is to figure out who Ann was IM-ing, what she
  sent, and recover evidence including
• 1. What is the name of Anns IM buddy?2. What
  was the first comment in the captured IM
  conversation?3. What is the name of the file Ann
  transferred?4. What is the magic number of the
  file you want to extract (first four bytes)?5.
  What was the MD5sum of the file?6. What is the
  secret recipe?

4
What protocol is being used?

• Remember that the count byte offset is 0.
• Look for bits that are commonly associated with a
  protocol.
• Example 0x0045 -gt beginning of an IPv4 packet
• Tcpdump from Anns Bad AIM packet capture

5
Wireshark - TCP

• IP protocol details displayed within Wireshark.
  Notice that the IP packet contains information
  about the encapsulated protocol (in this case,
  0x06, or TCP). Pg 85

6
TCp / udp port numbers

• http//www.iana.org/assignments/port-numbers
• /etc/services
• Example chunk of file

7
UDP port association

• UDP Protocol Details displayed within Wireshark.
  Notice that Wireshark automatically associates
  the UDP port, 123, with its IANA-assigned default
  service, NTP. Pg 86

8
Wireshark is not always correct

• TCP packet details displayed within Wireshark.
  Notice that Wireshark automatically associates
  TCP port 443 with its IANA-assigned default
  service, HTTPS. However, this interpretation is
  INCORRECT (as evidenced by the fact that the
  packet contents are not encrypted, and no
  protocol details are displayed under the heading
  Secure Socket Layer). Pg. 87

9
Find out about the mystery ip

• A simple whois lookup can provide a lot of
  information. Below is only a snippet of the data
  provided about IP address 64.12.24.50

10
Make a reasonable hypothesis

• Facts
• AOL provides services including HTTP and instant
  messaging
• Packet 112 source is port 5190, which Wireshark
  associates with AOL
• Packet begins with 0x4F465432, or OFT2 in ASCII
  which matches OSCAR protocol

11
OSCAR Protocol

• Byte 6 and 7 indicate type
• 0x0101 of packet 112 specifies the Prompt value
• Sender is ready to transmit file

12
Protocol decoding

• Message becomes clear when the protocol is decoded

13
Exporting fields

• Easy to do in Wireshark File gt Export Selected
  Packet Bytes
• Saves contents of selected fields for further
  study
• Tshark will print out any or all fields defined
  within the protocol
• Examples of command line instructions
• tshark -r evidence.pcap -X lua_scriptoft
  -tsk.lua -R "oft" -n -R frame.
• number 112 -V
• tshark -r evidence01.pcap -X lua_scriptoft
  -tsk.lua -R "oft" -n -R frame.
• number 112 -T pdml

14
Packet analysis

• Dirty word search using ngrep

15
Parsing Protocol fields

• Use tshark to extract all of the AIM message data
  from the package capture

16
Packet filtering

• Filtering with BPF
• Resulting file

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Find the file transfer

• Use Wireshark display filters to search for
  channel 2 ICBM packet sent to AOL server

18
Flow analysis

• List conversations
• List TCP flow

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Export TCP flow

• Once you have identified the flow most likely to
  contain the file, export it using a BPF filter
• Tcpflow will automatically extract flows, also
  using BPF filter
• Notice that tcpflow extracted two half-duplex
  flows

20
Export tcp flow continued

• Manually export using Wireshark
• Warning! Does not scale well, not good for large
  projects!
• Select Frame 109 gt Right click gt click on
  Follow TCP Stream
• Save in raw format

21
File and data carving

• Open full duplex saved dump file in hex editor
• First 4 bytes are OFT2
• Bytes 6-7 (Type) are 0x0101
• Bytes 28 31 (Total Size) are 0x00002EE8
• 12,008 bytes
• File name begins at Byte 192 0xc0
• Padded with null to 64 bytes
• Byte 256 new header
• 0x0202 acknowledge

22
File and data carving continued

• Look for magic number for beginning of .docx file
• 0x504B or PK in ASCII
• Byte 512 (0x200)
• To find the end of the file add the file size to
  the starting byte
• 0x0200 0x2EE8 0x30E8
• Byte 0x30E8 shows Type 0x0204 done
• Size of transfer Byte 0x3108 0x2EE8 which is a
  match to the file size

23
File and data carving continued again

• Use Bless cut tool to carve out the file
• Select extra data at the end of the file and
  click cut
• Select extra data at the beginning of the file
  and click cut
• Save file as recipe.docx
• Get cryptographic hashes of file
• Double check file size
• Verify the file type

24
Carved file

• Open a copy of the file to verify the contents

25
Extract file automatically

• Use tcpextract
• Uses 0x504B0304 by default to mark the beginning
  of a file
• Try saving the first instance 00000023.zip as
  recipe-tcpxtract.docx and open a copy in
  document editor
• Do not forget to take the cryptographic hashes

26
networkMiner

• All of the work is done for us in NetworkMiner

27
Disclaimer All information and data pulled
directly from this book. Pages 88 - 134

• Works Cited
• Davidoff, S., Ham, J. (2012). Network Forensics
  Tracking Hackers Through Cyberspace. Boston
  Prentice Hall.
•