CHAPTER 6

Security in Networks

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Objectives differentiate the security needs in the network and

in single ,stand alone application and environment identify threats against network applications,

including denial of service, web site defacements, malicious code and protocol attacks

explain various controls against network attacks such as physical security, policies and procedures and range of technical controls

Explain about design, capabilities and limitation of the firewall

Define and describe the intrusion detection systems and secure e-mails

(c) by Syed Ardi Syed Yahya Kamal, UTM 2004

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The Network Concepts

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When studying the chapter, student should know: The type of networks (LAN, MAN, etc) The size and shape Media (cable, wireless, optical cable, etc) Protocol (OSI layers, TCP/IP, etc) Topologies (star, ring, etc) Advantages of computing networks (resource

sharing, distributing the workload, etc)

Threats in Networks

What makes a network vulnerable?

Cause Explanation

Anonymity An attacker can mount an attack from thousand of miles away and safe behind electronic shield.

Many point of attack – both targets and origins

File stored in a network host can be access remotely by any user. Administrator can enforce many policies but one file being transferred through network, the policies means nothing.

Sharing Because networks enable resource and workload sharing, more user have the potential to access networked systems.

Complexity of system Operating System is a complicated piece of software but it is not designed specifically for security.

Unknown perimeter Network have no boundary. Resources on one network are accessible to the other network as well.

Unknown path Many paths can be used to accessed another host / computer.

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Threats in Networks (cont) We cannot list who attacks networks but we do

know what the motives of attacking.Motives Explanation

Challenge Someone skilled in writing or using programs – the single most significant motivation for a network attacker is the intellectual challenge. “Can I defeat the network?”

Fame Other attackers seek recognition for their activities. Enjoy the personal thrill of seeing their attacks written up in the news media.

Money and Espionage Seeking information on company’s product, clients etc. for financial reward

Ideology Hactivism : operations that use hacking techniques against a target’s (network) with the intent of disrupting normal operations but not causing serious damage.

Cyberterrorism : politically motivated hacking operation intended to cause grave harm such as loss of life or severe economic damage.

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Threats in Networks (cont)

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Threat precursor: Port scan

Program that give an information about three things: Which standard ports or services are running and responding? What operating system is installed? What applications and versions of applications are present?

Example:nmap scanner, netcat, Nessus, CyberCop Scanner

Social engineering Involves using social skills and personal interaction to get

someone to reveal security-relevant information and perhaps even do something that permits an attack. "Hello, this is John Davis from IT support. We need to test some

connections on the internal network. Could you please run the command ipconfig/all on your workstation and read to me the addresses it displays?" The request sounds innocuous . But unless you know John Davis and his job responsibilities well, the caller could be an attacker gathering information on the inside architecture.

Threats in Networks (cont)

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Threat precursor (cont): Reconnaissance

Gathering discrete bits of information from various sources and then putting them together like the pieces of a puzzle. Eavesdropping – follow employees to lunch and listen in

from nearby tables as coworkers discuss security matters.

Bulleting board and chats Numerous underground bulleting boards and chat

rooms support exchange of information. Attackers can post their latest exploits and techniques and

read what others have done.

Threats in Networks (cont)

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Threat precursor (cont): Availability of documentation

Vendor themselves sometimes distribute information that is useful to an attacker. Microsoft produces a resource kit by which application vendors

can investigate a Microsoft product in order to develop compatible, complementary applications.

Operating System and Application Fingerprinting can mark the manufacturer and version

attacker might use a Telnet application to send meaningless messages to another application. Ports such as 80 (HTTP), 25 (SMTP), 110 (POP), and 21 (FTP) may respond with something like Microsoft ESMTP MAIL Service, Version: 5.0.2195.3779

This reply tells the attacker which application and version are running.

Threats in Networks (cont)

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Threats in transit: Eavesdrop – implies overhearing without

expending any extra effort. Attacker monitoring all traffic passing through a node.

Wiretap – intercepting communications through some effort. Passive wiretapping is just "listening," much like

eavesdropping Active wiretapping means injecting something into

the communication Someone could replace your communications with his own

or create communications purported to be you. Works differently depending on communication medium

used.

Threats in Networks (cont)

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Impersonation: Impersonate another person or process In an impersonation, an attacker has several

choices Guess the identity and authentication details of the

target. Pick up the identity and authentication details through

eavesdropping or wiretapping. Use the target that will not be authenticated. Use a target whose authentication data are known.

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Spoofing Guessing or otherwise obtaining the network

authentication credentials of an entity Examples of spoofing are:

masquerading, session hijacking man-in-the-middle attacks

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Masquerade one host pretends to be another A variation of this attack is called phishing

send an e-mail message, perhaps with the real logo of Blue Bank, and an enticement to click on a link, supposedly to take the victim to the Blue Bank web site.

The enticement might be that your victim's account has been suspended (and need the account number and PIN to activate it), or some other legitimate-sounding explanation.

The link might be to your domain Blue-Bank.com, the link might say click here to access your account (where the click here link connects to your fraudulent site), or other trick with the URL to fool your victim, like www.redirect.com/bluebank.com.

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Session Hijacking intercepting and carrying on a session begun by

another entity Suppose two entities have entered into a session but

then a third entity intercepts the traffic and carries on the session in the name of the other

The attacker steals a valid session ID which is used to get into the system and snoop the data

*Tools:Juggernaut

HuntIP Watcher

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Man-in-the-Middle Attack one entity intrudes between two others difference between man-in-the-middle and

hijacking is that a man-in-the-middle usually participates from the start of the session, whereas a session hijacking occurs after a session has been established.

Tools:PacketCreator

Ettercap Dsniff

Cain e Abel

Message Confidentiality Threats

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An attacker can easily violate message confidentiality (and perhaps integrity) because of the public nature of networks.

Eavesdropping and impersonation attacks can lead to a confidentiality or integrity failure.

Several other vulnerabilities that can affect confidentiality. Misdelivery Exposure Traffic Flow Analysis

Message Integrity Threats

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the integrity or correctness of a communication is at least as important as its confidentiality.

Threats based on failures of integrity in communication. Falsification of Messages- an attacker can take

advantage of our trust in messages to mislead us change some or all of the content of a message replace a message entirely, including the date, time, and

sender/receiver identification

Noise -Signals sent over communications media are subject to interference from other traffic on the same media, as well as from natural sources

Fortunately, communications protocols have been intentionally designed to overcome the negative effects of noise

Web Site Vulnerabilities

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Web site is especially vulnerable because it is almost completely exposed to the user

One of the most widely known attacks is the web site defacement attack

Web site defacement attack Buffer Overflows Dot-Dot-Slash Application Code Errors Server-Side Include

Denial of Service

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There are many accidental and malicious threats to availability or continued service. Transmission Failure Connection Flooding

Echo-Chargen Ping of Death Smurf Syn Flood

Traffic Redirection DNS Attacks

Distributed Denial of Service

Smurf

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Figure 7-16. Smurf Attack.

Distributed Denial of Service

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Threats in Active or Mobile Code

Active code or mobile code is a general name for code that is pushed to the client for execution

related potential vulnerabilities: Cookies Scripts Active Code

Java Code ActiveX Controls

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Network Security Controls

Design and Implementation Architecture

Segmentation -Segmentation reduces the number of threats, and it limits the amount of damage a single vulnerability can allow. a web server, to handle users' HTTP sessions application code, to present your goods and services for purchase a database of goods, and perhaps an accompanying inventory to the count of stock on hand and being requested from suppliers a database of orders taken

Segmented Architecture.

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Figure 7-19. Segmented Architecture.

Redundancy -allowing a function to be performed on more than one node failover mode -the servers communicate with

each other periodically, each determining if the other is still active

Single Points of Failure-architecture should at least make sure that the system tolerates failure in an acceptable way

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Encryption

encryption is powerful for providing privacy, authenticity, integrity, and limited access to data

Encryption in network applications : either between two hosts (link encryption) between two applications (end-to-end encryption)

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link encryption -data are encrypted just before the system places them on the physical communications link

encryption occurs at layer 1 or 2 in the OSI model decryption occurs just as the communication arrives at and

enters the receiving computer Encryption protects the message in transit between two

computers, but the message is in plaintext inside the hosts the exposure occurs on the sender's or receiver's host or

workstation, protected by alarms or locked doors Link encryption is especially appropriate when the

transmission line is the point of greatest vulnerability. If all hosts on a network are reasonably secure but the communications medium is shared with other users or is not secure, link encryption is an easy control to use

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Link Encryption

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Figure 7-20. Link Encryption.

Figure 7-21. Message Under Link Encryption.

Message Under Link Encryption.

End-to-End Encryption

end-to-end encryption provides security from one end of a transmission to the other

encryption can be applied by a hardware device between the user and the host

the encryption can be done by software running on the host computer

encryption is performed at the highest levels (layer 7, application, or perhaps at layer 6, presentation) of the OSI model

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End-to-End Encryption

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Comparison of Link and End-to-End Encryption.

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Link Encryption End-to-End Encryption

Security within hosts

Data exposed in sending host

Data encrypted in sending host

Data exposed in intermediate nodes

Data encrypted in intermediate nodes

Role of user

Applied by sending host Applied by sending process

Invisible to user User applies encryption

Host maintains encryption User must find algorithm

One facility for all users User selects encryption

Typically done in hardware Either software or hardware implementation

All or no data encrypted User chooses to encrypt or not, for each data item

Implementation concerns

Requires one key per host pair

Requires one key per user pair

Provides node authentication

Provides user authentication

Virtual Private Networks Link encryption can be used to give a network's

users the sense that they are on a private network, even when it is part of a public network

the communication passes through an encrypted tunnel or tunnel

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PKI and Certificates

A public key infrastructure, or PKI , is a process created to enable users to implement public key cryptography, usually in a large (and frequently, distributed) setting.

PKI offers each user a set of services, related to identification and access control, as follows : Create certificates associating a user's identity with a

(public) cryptographic key Give out certificates from its database Sign certificates, adding its credibility to the authenticity

of the certificate Confirm (or deny) that a certificate is valid Invalidate certificates for users who no longer are allowed

access or whose private key has been exposed

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PKI sets up entities, called certificate authorities , that implement the PKI policy on certificates.

The specific actions of a certificate authority include the following: managing public key certificates for their whole

life cycle issuing certificates by binding a user's or system's

identity to a public key with a digital signature scheduling expiration dates for certificates ensuring that certificates are revoked when

necessary by publishing certificate revocation lists

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SSH Encryption

SSH (secure shell) is a pair of protocols (versions 1 and 2), originally defined for Unix but also available under Windows 2000, that provides an authenticated and encrypted path to the shell or operating system command interpreter

The SSH protocol involves negotiation between local and remote sites for encryption algorithm (for example, DES, IDEA, AES) and authentication (including public key and Kerberos ).

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SSL Encryption

The SSL (Secure Sockets Layer ) protocol was originally designed by Netscape to protect communication between a web browser and server

SSL interfaces between applications (such as browsers) and the TCP/IP protocols to provide server authentication, optional client authentication, and an encrypted communications channel between client and server.

To use SSL, the client requests an SSL session. The server responds with its public key certificate so that the client can determine the authenticity of the server

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IPSec

IPSec is implemented at the IP layer IPSec is somewhat similar to SSL, in that it

supports authentication and confidentiality (in applications) or below it (in the TCP protocols).

it was designed to be independent of specific cryptographic protocols and to allow the two communicating parties to agree on a mutually supported set of protocols.

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Packets: (a) Conventional Packet; (b) IPSec Packet.

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Figure 7-27. Packets: (a) Conventional Packet; (b) IPSec Packet.

signed code . A trustworthy third party appends a digital

signature to a piece of code, supposedly connoting more trustworthy code. A signature structure in a PKI helps to validate the signature.

Encrypted E-mail To protect the privacy of the message and routing

information, we can use encryption to protect the confidentiality of the message and perhaps its integrity.

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Strong Authentication

One-Time Password ChallengeResponse Systems Digital Distributed Authentication Kerberos

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Access Controls

Authentication deals with the who of security policy enforcement; access controls enforce the what and how ACLs on Routers Firewalls Honeypots

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(c) by Syed Ardi Syed Yahya Kamal, UTM 2004

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Target Vulnerability Precursors to attack     •Port scan

•Social engineering •Reconnaissance •OS and application fingerprinting

Authentication failures   •Impersonation •Guessing •Eavesdropping •Spoofing •Session hijacking •Man-in-the-middle attack

Programming flaws     •Buffer overflow

•Addressing errors •Parameter modification, time-of-check to time-of-use errors •Server-side include •Cookie •Malicious active code: Java, ActiveX •Malicious code: virus, worm, Trojan horse •Malicious typed code

Summary of Network Vulnerabilities

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Target Vulnerability Confidentiality     •Protocol flaw

•Eavesdropping •Passive wiretap •Misdelivery •Exposure within the network •Traffic flow analysis •Cookie

Integrity     •Protocol flaw

•Active wiretap •Impersonation •Falsification of message •Noise •Web site defacement •DNS attack

Availability     •Protocol flaw

•Transmission or component failure •Connection flooding, e.g., echo-chargen, ping of death, smurf, syn flood •DNS attack •Traffic redirection •Distributed denial of service

Summary of Network Vulnerabilities

Firewalls

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Firewall is a device that filters all traffic between a protected or “inside” network and a less trustworthy or “outside” network.

The purpose of a firewall is to keep “bad” things outside a protected environment.

To accomplish that, firewalls implement a security policy.

Firewalls (cont)

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The design of firewall should maintain below qualities: Always invoked. Tamperproof. Small and simple enough for rigorous analysis.

Firewalls (cont)

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Type of firewalls are depends on their capabilities. The type are: Packet filtering gateways or screening routers.

Most effective. Control packet from source to destination.

Stateful inspection firewalls. Maintains state infomation from one packet to

another in the input stream. Application proxies.

Simulate the (proper) effects of an application so that the application will receive only requests to act properly.

Firewalls (cont)

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Type of firewalls (cont): Guards.

Sophisticated firewall. Decide what services to perform on the user’s behalf in accordance with its available knowledge.

Personal firewall. An application program that runs on a workstation to

block unwanted traffic, usually from the network.

Comparison of Firewall Types

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Packet Filtering Stateful Inspection

Application Proxy Guard Personal Firewall

Simplest More complex Even more complex

Most complex Similar to packet filtering firewall

Sees only addresses and

service protocol type

Can see either addresses or data

Sees full data portion of packet

Sees full text of communication

Can see full data portion of packet

Auditing difficult Auditing possible Can audit activity Can audit activity Can and usually does audit activity

Screens based on connection rules

Screens based on information

across packetsin either header or

data field

Screens based on behavior of

proxies

Screens based on interpretation of

message content

Typically, screens based on

information in a single packet,

using header or data

Complex addressing rules

can make configuration

tricky

Usually preconfigured to

detect certain attack signatures

Simple proxies can substitute for

complex addressing rules

Complex guard functionality can limit assurance

Usually starts in "deny all

inbound" mode, to which user adds trusted addresses as they appear

Intrusion Detection Systems

An intrusion detection system (IDS ) is a device, typically another separate computer, that monitors activity to identify malicious or suspicious events

IDSs perform a variety of functions: monitoring users and system activity auditing system configuration for vulnerabilities and

misconfigurations assessing the integrity of critical system and data files recognizing known attack patterns in system activity identifying abnormal activity through statistical analysis managing audit trails and highlighting user violation of

policy or normal activity correcting system configuration errors installing and operating traps to record information about

intruders

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Types of IDSs Signature-based intrusion detection systems

perform simple pattern-matching and report situations that match a pattern corresponding to a known attack type

Heuristic intrusion detection systems, also known as anomaly based

Intrusion detection devices can be network based or host based A network-based IDS is a stand-alone device attached

to the network to monitor traffic throughout that network;

a host-based IDS runs on a single workstation or client or host, to protect that one host.

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Stealth Mode most IDSs run in stealth mode , whereby an IDS

has two network interfaces: one for the network (or network segment) being monitored and the other to generate alerts and perhaps other administrative needs

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Goals for Intrusion Detection Systems An IDS could use someor allof the following

design approaches: Filter on packet headers Filter on packet content Maintain connection state Use complex, multipacket signatures Use minimal number of signatures with maximum

effect Filter in real time, online Hide its presence Use optimal sliding time window size to match

signatures

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IDS Strengths and Limitations Intrusion detection systems are evolving products detect an ever-growing number of serious

problems.

its sensitivity which is difficult to measure and adjust

someone has to monitor its track record and respond to its alarms

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EXERCISE

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Discuss six reasons that makes network vulnerable.

One way an attacker can do to investigate and plan the attack is through reconnaissance. Explain about it.

What firewalls can and cannot block? Explain detail about Kerberos?