Packet AnalysisLisa BockPennsylvania College of Technology

Topics Covered

• Overview of Packet Analysis• The OSI Model• The TCP/IP Protocol Suite

– Normal Network Communication - TCP and UDP• Abnormal Communication

– Scanning– Malware

Overview of Packet Analysis• Packet analysis uses a packet sniffer, network monitor or

analyzer, to monitor and troubleshoot network traffic. • As data flows across the network, the sniffer captures

each packet decodes the packet's raw bits – Showing the field values in the packet according to the

appropriate RFC or other specifications.• The information can identify bottlenecks and help

maintain efficient network data transmission.

Uses for Packet Analysis• Analyze network problems• Detect network intrusion attempts and network misuse • Perform regulatory compliance through content

monitoring perimeter and endpoint traffic• Monitor bandwidth utilization • Verify endpoint security status• Gather and report network statistics

Common Packet Analyzers• Capsa Network Analyzer• Cain and Abel• Carnivore (FBI - monitors all of a target user's Internet traffic) • dSniff• ettercap• Microsoft Network Monitor• ngrep, Network Grep• OmniPeek• Snoop• Tcpdump• Wireshark (formerly known as Ethereal)• Xplico Open source Network Forensic Analysis Tool

Xplico

Packet Capture• Traffic captured is dependent on the placement of

the device.• On a switch, the packet sniffer will see only data

going to and from the switch to the capture device• Traffic seen will be unicast, broadcast, or multicast.• To see all traffic, port monitoring or SPAN on a switch

is used, or use a full duplex tap in line with traffichttp://wiki.wireshark.org/CaptureSetup/Ethernet

The OSI Model

• In order to understand packet analysis you must understand the way data is prepared for transit.

• The OSI model, is a seven-layer representation of how data changes in form as each layer provides services to the next layer – Data encapsulates or de-encapsulates

The OSI Model

MAC

Port

IP

Address

Data

Frame

Segment

Packet

PDU

Bits

Wireshark• The tool we will use for demonstration is Wireshark

http://www.wireshark.org , formerly Ethereal, an open-source packet analyzer.

• Download and install Wireshark – make sure you install WinPCap (Windows Packet Capture) if you are using Windows

• For a live capture, launch Wireshark and click the name of an interface under Capture Interfaces to start capturing packets on that interface.

Wireshark

Configure advanced features by clicking OptionsSelect the interface with active packet exchange

The OSI Model

• In Wireshark, select any TCP frame and you will see the frame contents from layer 2-7

Data

Frame

Segment

Packet

For a review go to http://wiki.wireshark.org/Ethernet

Help in Wireshark

Easily find help in Wireshark-including Sample Captures

Capture Packets• We will be use pre-captured packets found in your

folder and review they normal traffic versus abnormal traffic

• Once you open a capture you will see three panes:– The Packet List view - a list of all of the packets received

during the capture session. – The middle window is the Details view.– The bottom is the individual Packet Bytes

TCP Example

• Normal traffic• Three-way handshake packets 1,2,3• Review port numbers, flags, SEQ ACK numbers,

stream index• Packets 38-39 FIN packets• Packet 4 get image: File->export objects

http://www.symantec.com/connect/articles/studying-normal-traffic-part-three-tcp-headers

UDP Example Provides connectionless Transport Layer service

to other applications on the internet without having to go through a handshake or connection process.

It is a simple protocol and that does not provide any ordering or data integrity services.

UDP is an unreliable service. Few problems occur with UDP.

What uses UDP? Commonly used in video streaming and time-

sensitive applications. UDP Applications:

Domain Name System (DNS) Voice over IP (VoIP) Trivial File Transfer Protocol (TFTP) Domain Host Configuration Protocol (DHCP) Routing Information Protocol (RIP)

DNS• Filter UDP and you will see the DNS packets• Convert symbolic host names such (google.com) to

an IP address (72.14.204.103)• Transfers name information between DNS servers

• DNS uses TCP in a zone transfer

• Look up other host names such as mail exchange (MX) records

• DNS is essential to any network

Normal DNS Queries/Responses• Client sends query to DNS server for an IP address• Server responds with information it has or asks

other DNS servers for the information• All DNS packets have four (4) sections:

– Questions– Answer Resource Records– Authority Resources Records– Additional Resource Records

DNS Packet Structure - Flags

If RD is set, it directs the name server to pursue the query recursively.

• With Fast Flux, a fully qualified domain name will have multiple IP addresses assigned to it.

• It manipulate the way the domain name system works and takes advantage of the way load balancing is built into the domain name system.

• A botnet can be created with nodes that join and drop off the network and evade capture.

Fast Flux DNS Evasion

Fast Flux DNS• Criminals use a sixty-second time-to-live (TTL) setting for

their DNS resource records and swapping the records' associated IP addresses in and out with extreme frequency.

FTP – Grab a Pic• Purpose of FTP is to transfer files over TCP • Uses both ports 20 and 21

– Command channel is designated on port 21 for the FTP server.

– To transfer data like directory contents or files, a secondary channel, port 20 is used.

• Filter FTP-data traffic - then follow the TCP stream. Save as .jpg

Reassemble the Streams

• Can reassemble and obtain content if data is not encrypted

• Filter ftp-data traffic• Right click follow TCP stream and save the file as

raw data and click save as mystery.jpg• Go to where you saved the file and open it!

Internet Control Message Protocol

• ICMP is used by routers, intermediary devices, or hosts to communicate updates or error information to other routers, intermediary devices, or hosts.– Used to troubleshoot network issues– Not used to exchange data between systems

• ICMP is used by ping because it can generate echo-request/echo-reply query messages.

A Scout for IP!

Internet Control Message Protocol• Four types of query messages that characterize the

output generated by the ping command. – Echo request/echo reply: Used to test reachability– Time stamp request/time stamp reply: Used to compute delay

between time stamps– Information request/information reply: Locates address of local

IP network– Subnet mask request/subnet mask reply: Subnet information is

exchange

ICMP-Dest Unreachable

• RFC 792 –” ICMP is actually an integral part of IP, and must be implemented by every IP module.”

ICMP Error Codes• Type 3 Destination Unreachable Codes

– 0 - Net Unreachable– 1 - Host Unreachable– 2 - Protocol Unreachable

• Type 5 Redirect Codes– 0 – Redirect Datagram for Network– 1 – Redirect Datagram for Host– 2 - Redirect Datagram for Type of Service

• Type 11 Time Exceeded Codes– 0 – TTL Exceeded– 1 – Fragment Reassembly Time Exceeded

• Type 12 Parameter Problem Codes– 0 – Pointer Indicates the Error– 1 – Missing Required Option– 2 - Bad Length

ICMP - Errors

• Frame 5 Destination unreachable port unreachable snmp 161

• A response with a nested packet – We have the IP header to send the packet to the target – After the destination unreachable message returns it

sends back the IP header and 64 bits of original datagram• ICMP is used in reconnaissance by Kali Linux

http://it-ebooks.info/book/3000/

BAD Connection• Diagnose performance problems

– Use Wireshark's expert system and coloring rules• High latency can be from:

– Processing delays– Distance– Queuing delays (BUFFERBLOAT)

• Buffers to fill up and remain full at congested links, contributing to excessive traffic delay and losing the ability to perform their intended function of absorbing bursts.

Identify High Latency Times• In this trace file you can

identify delays– First filter on conversations

Go to-Statistics then Conversations

– Select IPv4 tab SORT Bytes A->B

– Right click Apply as a Filter ->Selected A->B

Identify High Latency Times• Set the Time column to Seconds since Previously Displayed

Packet – Sort highest to lowest and you will see:– Retransmissions- Dup ACK’s, Keep-Alives

Expert System• Using Wireshark’s Expert

System to help Identify problems– Clear filter– Lower left hand corner click

on the red circle to bring up the expert system

Zero Window

• If the client advertizes a zero window, the application is unable to process quickly enough from the TCP receive buffers. Packet 298

Network Scans

• Nmap is a tool used to discover hosts and services on a network, and create a "map" of the network.– It can be either legitimately or maliciously used to quickly

scan thousands of ports, and discrimination between ports in open, closed and filtered states.

• By default, Nmap performs a SYN Scan, which works against any TCP stack.

Nmap• Scanning can be used as a passive attack in the form of reconnaissance.

• After running a scan, the software will output results from the IP range

you selected:– PortslHosts - the results of the port scan, including the well-known services for

those ports. – Topology - an interactive view of the connections between hosts in a network. – Host Details – Details such as the number of ports, IP addresses, hostnames,

operating systems, and more.

Scan – SYN• Same source and

destination IP address• Only the SYN flag is set• The destination port

numbers of each packet changes as it tries every port

http://www.symantec.com/connect/articles/network-intrusion-detection-signatures-part-two

Scan - ARP

• An arp-scan sends ARP packets to hosts on the local network and displays any responses that are received. – ARP packets are not routable

• An advantage of ARP scanning is discovering hosts behind a firewall

Detecting an ARP Scan• Detecting can be difficult if the scanning software is not scanning at a

high speed• Below find a comparison of a normal capture to an ARP scan – the

right shows a higher packet rate

SCAN - Port

• Full Connect Scan• TCP connect scan is the default TCP scan type when

SYN scan is not an option.• A TCP Reset response indicates the port is closed

SCAN - Port• Packets 18, 19 and 20 we see an actual connection• Then it continues to attempt another connection in Packet

21

SEC-Bittorrent• BitTorrent uses a distributed sloppy hash table (DHT) for storing peer

contact information for "trackerless" torrents.• DHT consists of a number of different queries and corresponding

responses. – Ping G used to check if a peer is available.– Find_node G used to find the contact information for a peer.– Get_peers G requests a list of peers which have pieces of the content.– Announce_peer G announces the contact information for the peer to the

network.Right click on packet 22 and follow

UDP Stream

Ettercap

• Ettercap is an open source tool used to perform a man-in-the-middle attack in a switched environment

• Once Ettercap has inserted itself in the middle of a connection, it can capture and examine all communication between the two victims, and launch an attack - such as a DNS spoof

SEC-ettercap-poisoner• Ettercap also has the ability to actively or passively

find other poisoners on the LAN.• This trace file has the signature of Ettercap’s 'Check

for Poisoner' function. – Go to the IP header - > ID field of a ping packets contains

the signature 0xe77e which is ‘ette’ in Leet speak– Systems that answer back with the same IP ID value are

most likely running Ettercap as well.

Fragmentation Scanning • A scanning technique that fragments IP packets during the

port scan in an attempt to bypass some firewall devices.• Instead of just sending the probe packet, it is broken into a

couple of small IP fragments.• Splitting up the TCP header over several packets to make it

harder for packet filters and IDS to detect. – This method won't work with packet filters and firewalls that

queue IP fragments and can cause some systems to crash

Fragmentation Scanning

• Not an attack tool itself, rather it is a technology that allows other attacks to avoid detection by network intrusion detection systems.

NOTE: Fragmentation of a packet should rarely occur since MTU discovery techniques now exist.

SEC-nmap-fragscan• This trace file depicts a

system sending an IP fragment scan.

• If you examine the IP header, the protocol field indicates that TCP follows.

• Manually decode the TCP header to identify the purpose of the TCP packets.

Configure your

devices!

SEC-nmap-ipscan• nmap-ipscan is an IP scan

used to determine what services are supported directly on top of the IP header. – IRDP, ICMP, EGP.

• Sort Info column heading to see a list of protocols queried.

More Resources • For more Packet Captures go to

http://www.netresec.com/?page=PcapFiles• Wireshark Network Analysis, by Laura Chappell,

Chappell Binding Paperback ISBN 978-1-893939-99-8• Practical Packet Analysis: Using Wireshark to Solve

Real-World Network Problems, by Chris Sanders, No Starch Press, Incorporated ISBN-13: 9781593272661 2010