1. Review Exam 2
Spring 2016

2. Targeted Break-in, DoS, & Malware attacks (I)

3. 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 s
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.
* Electronic Data Gathering, Analysis, and Retrieval

4. Host Scanning Objective: identify IP addresses of active hosts
Pinging individual hosts
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

5. 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

6. Port Scanning Port Scanning
Most break-ins exploit specific services/applications
Service Default Port www 80 FTP 21 SMTP 25
Scan target for open ports
Send SYN segments to a particular port number
Observe SYN/ACK or reset (RST) responses

7. 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

8. 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
(8 bits)
Protocol (8 bits)
1=ICMP, 6=TCP,17=UDP
Window Size
(16 bits)

9. 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

10. 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?
Active learning
Network scanning
Passive fingerprinting
None of the above

11. 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

12. 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? 4
1024
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.

13. Targeted Break-in, DoS, & Malware attacks (II)

14. TCP opening and DoS
Server 1 .
SYN
Waiting for request from Computer 1
SYN/ACK
ACK 2
SYN
Waiting for request from Computer 2
SYN/ACK
ACK 3
SYN
Waiting for request from Computer 3
SYN/ACK
ACK .
For each TCP connection request (SYN), server has to:
Respond to the request (SYN/ACK)
Set resources aside in order respond to each data request

15. Denial of Service (DoS)
Attacker’s Home Network
What resources the web server would use to respond to each of the HTTP requests it receives?
What could be the consequences of the web server being invaded by too much requests from the attacker?

16. 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

17. 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

18. Fragment Offset (13 bits)
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 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:
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 < bytes
Fragment offset: identify which fragment this packet is attached to. Flags: indicates whether packet could be fragmented or not

19. Teardrop attacks Take advantage of IP fragmentation
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
Victim
* Win 3.1, Win 95, Win NT, and Linux prior to 2.163

20. 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 Server

21. 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?
LAND attack
Teardrop
Ping of Death
None of the above
In which of the following DoS attacks the attacker makes use of IP spoofing?

22. 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

23. 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
Victim

24. 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

25. 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
Bots
Attack
Command
Server
Handler
Attacker
Attack
Command
DoS Messages
Link to how to deal with DDoS (by Cisco)

26. Distributed DoS (DDoS) Attack

27. Distributed DoS (DDoS) Attack

28. Malware Attacks

29. Malware attacks Types of malware: Viruses Worms Trojan horses
Logic bombs

30. Virus Code/Program (script, macro) that: attaches to files Symptoms:
Spreads by user actions (floppy disk, flash drive, opening 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.

31. 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”.
Stealth OS
* metamorphic engine is needed

32. Question: Distinguish between viruses and worms
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

33. Trojan horse A computer program When executed, a Trojan horse could
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

34. 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 months after the name removal.

35. Firewalls 35

36. Test your Firewall knowledge
Which of the following is true about firewalls?
A firewall is a hardware device
A firewall is a software program
Firewalls could be hardware or software
They are used to protect a whole network against attacks
They are used to protect single computers against attacks
Both a and b.

37. Test your Firewall knowledge (cont)
Which of the following is true about firewalls?
They are configured to monitor inbound traffic and protect against attacks by intruders
They are configured to monitor outbound traffic and prevent specific types of messages from leaving the protected network.
Both a and b

38. Firewall: definition
Hardware or software tool used to protect a single host1 or an entire network2 by
“sitting” between a trusted network (or a trusted host) and an untrusted network
Applying preconfigured rules and/or traffic knowledge to allow or deny access to incoming and outgoing traffic
Trusted network
PC with Host-based Firewall
Untrusted network
Network-Based Firewall
1 Host-based or personal firewall 2 network-based firewall

39. Questions
What is the main advantage of having a host-based firewall in addition to having a network-based one?
Answer:_________________________________________
What kind of security issue could be associated with having host-based firewall on users PCs?
Answer:__________________________________________
Trusted network
PC with Host-based Firewall
Untrusted network
Network-Based Firewall

40. Firewall Architecture
Most firms have multiple firewalls. Their arrangement is called the firm’s
firewall architecture
Firewall Architecture
Internet
Main Border Firewall
x Subnet
Marketing Client on x Subnet
Accounting Server on x Subnet
Public Webserver
SMTP Application Proxy Server
HTTP Application Proxy Server
External DNS Server
Screening Router
Firewall
Internal
Host
Server on x Subnet
Demilitarized Zone (DMZ)

41. Questions
What is a DMZ?
Which of the following may be placed in a DMZ?
A SMTP proxy server
A server that contains files available for downloading by employees
An File Transfer Protocol server
A SQL (Structured Query Language) database server
What IP addresses should a DNS server in the DMZ be able to find?
All company’s IP addresses
Only the IP addresses of the computers in the internal subnet
Only the IP addresses of the computers in the DMZ
You work as the security administrator at King.com. King.com has been receiving a high volume of attacks on the king.com web site. You want to collect information on the attackers so that legal action can be taken. Which of the following can you use to accomplish this?
A DMZ (Demilitarized Zone).
A honey pot.
A firewall.
None of the above.

42. Basic Firewall Operation
Passed Packet
(Egress)
Passed Legitimate
Packet (Ingress)
Legitimate Packet 2
Legitimate Packet 1
Attack Packet 1
1. Internet
(Not Trusted)
Legitimate Packet 1
Legitimate Packet 2
Attacker
Border
Firewall
Attack Packet 1
Legitimate
User
Dropped Packet
(Ingress)
Egress filtering: filtering packets leaving to external networks
Ingress filtering:
filtering packets coming from external networks
Log
File
Internal Corporate Network (Trusted)

43. Application Layer Message
IP-H
TCP-H
UDP-H
Application Layer Message
Types of Firewalls
Static Packet Filtering Firewalls (1st generation)
Inspect TCP, UDP, IP headers to make filtering decisions
Do static filtering of individual packets based on configured ruleset (or Access Control List)
Prevent attacks that use IP or port spoofing, etc.
Stateful Packet Filtering Firewalls (2nd generation)
Do stateful filtering by checking the firewall’s state table for relation of packets to packets already filtered
If packet does not match existing connect, ruleset (static filt.) is used
If packet matches existing connection, it is allowed to pass
Prevent SYN attacks, teardrops, etc.
State Table
Connection
Source IP
Destination IP
State
Connection 1
:80
TCP opening
Connection 2
Data transfer ……
……….
………

44. Types of Firewalls (cont.)
IP-H
TCP-H
UDP-H
Application Layer Message
Types of Firewalls (cont.)
Application Firewalls (3rd generation)
Also called proxy firewalls
Inspect the Application Layer message (e.g. HTTP requests, s, etc.
Specialized proxy firewalls more effective than general-purpose
HTTP proxy firewalls for HTTP requests
SMTP proxy firewalls for SMTP s
FTP proxy firewall for FTP-based file transfer requests
Prevent malware attacks
HTTP
Proxy
2. Passed inspected
HTTP Request
1. HTTP Request
Browser
4. Passed inspected
HTTP Response
3. HTTP
Response
Webserver
Application
Log
File

45. Types of Firewalls (cont.)
Network Address Translation Firewall
Replace IP address in outgoing message by a spoof IP address
Hide internal hosts’ IP address to outsiders
Help prevent IP spoofing attacks using internal IP addresses
Host IP Address
Outgoing IP Address
Request ID
120121
120122
120123
……..
………