Transcript Review Exam 2

Review Exam 2
Spring 2013
Targeted Break-in, DoS,
& Malware attacks (I)
Unobtrusive Information
Collection
 Sending packets into a network is “noisy”
 Need to do unobtrusive info gathering, first, by
 Visiting target corporate website for
 Employees’ names and emails
 Officers names and organizational structure, etc.

Reading trade press (often online & searchable) for
 Info about products under development
 Firms’ financial prospects, etc.

Searching U.S. EDGAR* system online for
 Ownership, shareholder information, etc.

Searching the Whois database at:

NetworkSolutions.com/whhois/index.jsp, internic.net/whois.html, etc.
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* Electronic Data Gathering, Analysis, and Retrieval
Host Scanning
 Objective: identify IP addresses of active hosts
 Pinging individual hosts
Ping scanning

Pinging a range of IP addresses

IP scanning software: fping, gping, Ping Sweep, Pinger
 SYN/ACK scanning used when firewall configured to
block pinging from outside
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Network Scanning
 Objective: understand a network internal
structure including routers, firewalls location
 Also called network mapping
 Main tools used

Tracert (in Windows) or Traceroute (in Linux)

Network scanning software, e.g NetScanner
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Port Scanning
 Port Scanning

Most break-ins exploit specific
services/applications
Service
www
FTP
SMTP

Default Port
80
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Scan target for open ports


Send SYN segments to a
particular port number
Observe SYN/ACK or reset
(RST) responses
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Fingerprinting
 Determining specific software run by target


Identify a particular operating system or
application program and (if possible) version

For example, Microsoft Windows 2000 Server

For example, BSD LINUX 4.2

For example, Microsoft IIS 5.0
Useful because most exploits are specific to
particular programs or versions
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Active vs. Passive fingerprinting
 Active Fingerprinting

Send odd messages and observe replies

Different operating systems and application programs respond
differently

Active fingerprinting may set off alarms

Attackers usually use rate of attack messages below IDSs volume
thresholds
 Passive Fingerprinting

Read headers (IP-H, TCP-H, etc.) of normal response messages


e.g. Windows 2000 uses TTL = 128 and Window Size = 18000
Passive Fingerprint difficult b/c Admin could change default values
Time To Live
Protocol (8 bits)
1=ICMP, 6=TCP,17=UDP
(8 bits)
Window Size
(16 bits)
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Fingerprinting by reading banners
 Many programs have preset banners used in
initiating communications
 Using telnet or FTP to connect to a server could
display the banner
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Summary Questions 1 (cont.)

In preparing his attack, the attacker sent normal
HTTP requests to a web server. Then, he spent
some time analyzing the protocol-related
information in the response received from the web
server in order to determine what software are
installed on the web server. Which of the following
did the attacker do?
a)
b)
c)
d)
Active learning
Network scanning
Passive fingerprinting
None of the above
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Password guessing
 Brute force

Generating possible password combinations
by changing one character at a time

If password is 4 decimal numbers
 Start with 0000; next try 0001; then 0002; etc.
 How many possible combinations? ___________


If password is 6 alphabetical characters, how
many possible combinations? _____________
Brute force password cracking software
available
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Summary Questions 2 (cont.)


Assume that a password is 2 decimal number long.
What is the maximum number of passwords that an
attacker would have to try in order to crack the
password?
a) 4
b) 67108864
c) 1024
d) None of the above
How much time (in minutes) will it take to crack the
password if it requires 1.2 second to try each
password?
Answer: a maximum of ______ minutes.
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Targeted Break-in, DoS,
& Malware attacks (II)
TCP opening and DoS
Server
1
SYN
SYN/ACK
ACK
Waiting for request
from Computer 1
2
SYN
SYN/ACK
ACK
Waiting for request
from Computer 2
3
SYN
SYN/ACK
ACK
Waiting for request
from Computer 3
.
.
.
...
.
 For each TCP connection request (SYN), server has to:


Respond to the request (SYN/ACK)
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Set resources aside in order respond to each data request
Denial of Service (DoS)
Intel Pentium 4 540 (3 Ghz)
512 MB SDRAM
2 x 100 GB SATA HDD
16x CD Drive
Gateway 3-button mouse
Gateway 108 keyboard
SVGA graphic card
NetworkNetwork
Attacker’sHome
Home
Legitimate user
Legitimate user
HTTP requests
Workstation
Stream of HTTP requests
Workstation
Internet
Router
Hub
Workstation
Web Server
HTTP requests
All workstations use IP spoofing
to send HTTP requests to the
web server.
Legitimate user
Workstation
Workstation
Legitimate user


What resources the web server would use to respond to each of the HTTP requests it
receives?
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What could be the consequences of the web server being invaded by too much requests
from the attacker?
Denial of Service (DoS) Attack
 Attack that makes a computer’s resources
unavailable to legitimate users
 Types of DoS attacks:
 Single-message
DoS
 Flooding
DoS
 Distributed DoS
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Single-message DoS attacks
 First kind of DoS attacks to appear
 Exploit weakness in the coding of operating
systems and network applications
 Three main single-message DoS:



Ping-of-Death
Teardrop
LAND attack
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Total Length (16 bits)
Flags
Fragment Offset (13 bits)
Ping of Death attacks
 Take advantage of


Fact that TCP/IP allows large packets to be fragmented
Some network applications & operating systems’ inability to handle
packets larger than 65536 bytes
 Attacker sends IP packets that are larger than 65,536
bytes through IP fragmentation.
 Ping of death attacks are rare today as most operating
systems have been fixed to prevent this type of attack
from occurring.
 Example of PoD code and vulnerable Operating Systems:

http://insecure.org/sploits/ping-o-death.html
 Fix


Add checks in the reassembly process or in firewall to protect hosts with
bug not fixed
Check: Sum of Total Length fields for fragmented IP is < 65536 bytes18
Fragment offset: identify which fragment this packet is attached to. Flags: indicates whether packet could be fragmented or not
Total Length (16 bits)
Flags
Fragment Offset (13 bits)
Teardrop attacks




Take advantage of IP fragmentation
Attacker sends a pretend fragmented IP packet
But Fragment Offset values are not consistent
Earlier operating systems* and poorly coded
network applications crash because

Unable to reassemble the packet due to missing
fragments
Pretend fragmented IP packet
Frag 1
Frag 2
Frag 4
Attacker
* Win 3.1, Win 95, Win NT, and Linux prior to 2.163
Victim
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LAND attacks
 First, appeared in 1997
 Attacker uses IP spoofing with

source and destination addresses referring to target itself.
 Back in time, OS and routers were not designed to deal with this
kind of loopback
 Problem resurfaces recently with Windows XP and Windows 2003
Server
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Summary Questions 1


Do DoS attacks primarily attempt to jeopardize confidentiality,
integrity, or availability?
Which of the following DoS attacks takes advantage of IP
fragmentation?
a)
b)
c)
d)

LAND attack
Teardrop
Ping of Death
None of the above
In which of the following DoS attacks the attacker makes use
of IP spoofing?
a)
b)
c)
d)
LAND attack
Teardrop
Ping of Death
None of the above
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Flooding DoS Attacks
 Flood a target with a series of messages in
an attempt to make it crash
 Main types of flooding DoS attacks:




Flooding with regular requests
SYN flooding
Smurf flooding
Distributed DoS
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SYN Flooding
 Attacker sends a series of TCP SYN opening requests
 For each SYN, the target has to
 Send back a SYN/ACK segment, and
 set aside memory, and other resources to respond
 When overwhelmed, target slows down or even crash
 SYN takes advantage of client/server workload
asymmetry
SYN
SYN
SYN
SYN
SYN
Attacker
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Victim
Smurf Flooding DoS
 Attacker uses IP spoofing
 Attacker sends ping / echo messages to third
party computers on behalf of the target
 All third party computers respond to target
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Distributed DoS (DDoS) Attack
 Attacker hacks into multiple clients and plants handler programs on
them. Clients become bots or intermediaries
 Attacker sends attack commands to handlers which execute the
attacks
 First appeared in 2000 with Mafiaboy attack against cnn.com,
ebay.com, etrade.com, yahoo.com, etc.
Attack
Command
DoS Messages
Attack
Command
Bots
Server
Handler
DoS Messages
Attacker
Attack
Command
Link to how to deal with DDoS (by Cisco)
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Distributed DoS (DDoS) Attack
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Distributed DoS (DDoS) Attack
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Malware Attacks
Malware attacks
 Types of malware:
Viruses
Worms
Trojan horses
Logic bombs
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Virus
 Code/Program (script, macro) that:
 attaches to files
 Spreads by user actions (floppy disk, flash drive,
opening email attachment, IRC, FTP, etc), not by
themselves.
 Symptoms:
 Annoying actions when the virus is executed: hog up
memory, crash the system, drives are not accessible,
antivirus disabled, etc.
 Performing destructive actions when they are executed:
delete files, alter files, etc.
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Viruses
 Could be
 Boot sector viruses: attach themselves to files in boot
sector of HD
 File infector viruses: attach themselves to files (i.e.
program files and user files)
 Polymorphic viruses: mutate with every infection
(using encryption techniques), making them hard to
locate
 Metamorphic viruses: rewrite themselves completely
each time they are to infect new executables*
 Stealth: hides itself by intercepting disk access
requests by antivirus programs.
Request by antivirus
The stealth returns an uninfected version of files to the
anti-virus software, so that infected files seem "clean”.
* metamorphic engine is needed
Stealth
OS
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Worm
 Does not attach to files
 A self-replicating computer program that
propagate across a system
 Uses a host computer’s resources and network
connections to transfer a copy of itself to another
computer
 Harms the host computer by consuming
processing time and memory
 Harms the network by consuming the bandwidth
Question: Distinguish between viruses and worms
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Trojan horse
 A computer program
 That appears as a useful program like a game, a
screen saver, etc.
 But, is really a program designed to damage or
take control of the host computer
 When executed, a Trojan horse could
 Format disks
 Delete files
 Open TCP ports to allow a remote computer to
take control of the host computer (Back Door)
 NetBus and SubSeven used to be attackers’
favorite programs for target remote control
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Logic bomb
 Piece of malicious code intentionally inserted
into a software system
 The bomb is set to run when a certain condition
is met


Passing of specified date/time
Deletion of a specific record in a database
 Example: a programmer could insert a logic
bomb that will function as follow:


Scan the payroll records each day.
If the programmer’s name is removed from payroll,
then the logic bomb will destroy vital files weeks or
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months after the name removal.