Computer Network Research Group ITB Security Issues Onno W. Purbo Computer Network Research Group Institute of Technology Bandung [email protected]

Computer Network Research Group ITB

Security Issues

Onno W. Purbo

Computer Network Research Group

Institute of Technology Bandung

[email protected]


Perspective ...

less then 200 security incident in 1989. about 400 in 1989. about 1400 in 1993. estimated more than 2241 in 1994. Nobody knows the correct statistics on how

many attacks are actually detected by the sites broken into.


Layout Firewall

InterNet

InternalNetwork

Firewall


What are you trying to protect?

Your Data. Your Resources. Your Reputation.


What Are You Trying To Protect Against?

Type of attacks

Intrusion. Denial of Service. Information Theft.


Type of Attackers

Joyriders. Vandals. Score Keepers. Spies (Industrial & Otherwise). Stupidity & Accidents.


How Can You Protect Your Site

No Security. Security Through Obscurity. Host Security. Network Security. No Security Model Can Do It All.


What Can A Firewall Do?

A firewall is a focus for security decisions. A firewall can enforce security policy. A firewall can log Internet activity

efficiently. A firewall limits your exposure.


What Can’t A Firewall Do?

A firewall can’t protect you against malicious insiders.

A firewall can’t protect you against connections that don’t go through it.

A firewall can’t protect against completely new threats.

A firewall can’t protect against viruses.


List of A Must Secure Internet Services

Electronic mail (SMTP). File Transfer (FTP). Usenet News (NNTP). Remote Terminal Access (Telnet). World Wide Web Access (HTTP). Hostname / Address lookup (DNS).


Security Strategies. Least Privilege. Defense in Depth (multiple security mechanism). Choke Point forces attackers to use a narrow

channel. Weakest Link. Fail-Safe Stance. Diversity of Defense. Simplicity.


Building Firewalls


Some Firewall Definitions

Firewall– A component or set of components that restricts

access between a protected network and the Internet, or between other sets of networks.

Host– A computer system attached to a network.


Firewall Def’s Cont’ ..

Bastion Host– A computer system that must be highly secured

because it is vulnerable to attack, usually because it is exposed to the Internet and is a main point of contact for users of internal networks.

Dual-homed host– A general-purpose computer system that has at

least two network interfaces (or homes).


Firewall Def’s Cont ... Packet.

– The fundamental unit of communication on the Internet. Packet filtering.

– The action a device takes to selectively control the flow of data to and from a network.

Perimeter network.– a network added between a protected network and

external network, to provide additional layer of security.


Firewall Def’s Cont ...

Proxy Server– A program that deals with external servers on

behalf of internal clients. Proxy client talk to proxy servers, which relay approved client requests on to real servers,and relay answer back to clients.


Packet Filtering

InterNet

InternalNetwork

Routes or blocks packets,as determined by site's

security policy.

ScreeningRouter


Proxy Services

InterNet

InternalNetwork

Proxy ServerDual homed HostFirewall

Internal HostProxy Client

External HostReal Server


Screened Host Architecture

InterNet

InternalNetwork

ScreeningRouter

Bastion Host

Firewall


De-Militarized Zone Architecture

InterNet

InternalNetwork

PerimeterNetwork

Interior RouterChoke Router

Exterior Router

Bastion Host

Firewall


DMZ With Two Bastion Hosts

InterNet

InternalNetwork

PerimeterNetwork

Interior RouterChoke Router

Exterior Router

Firewall

SMTP / DNS Host

FTP/WWW Host


It’s OK

Merge Interior & Exterior Router Merge Bastion Host & Exterior Router Use Mutiple Exterior Router Have Multiple Perimeter Network Use Dual -Homed Hosts & Screened

Subnets


It’s Dangerous

Use Multiple Interior Router Merge Bastion Host and Interior Router


Private IP Address

Use within Internal Network Reference RFC 1597 IP address alocation:

– Class A: 10.x.x.x– Class B: 172.16.x.x - 172.31.x.x– Class C: 192.168.0.x - 192.168.255.x


Bastion Host

It is our presence in Internet.

Keep it simple. Be prepared for the bastion host to be

compromised.


Special Kinds of Bastion Hosts

Nonrouting Dual-Homed Hosts. Victim Machine. Internal Bastion Hosts.


Choosing A Bastion Host

What Operating System?– Unix

How Fast a Machine?– 386-based UNIX.– MicroVAX II– Sun-3


Proxy Systems

Why Proxying?– Proxy systems deal with the insecurity

problems by avoiding user logins on the dual-homed host and by forcing connections through controlled software.

– It’s also impossible for anybody to install uncontrolled software to reach Internet; the proxy acts as a control point.


Proxy - Reality & Illusion

User's Illusion

Percieved Connection

Actual Connection

Client

ServerProxy Server


Advantages of Proxying

Proxy services allow users to access Internet services “directly”

Proxy services are good at logging.


Disadvantages of Proxying Proxy services lag behind non-proxied services. Proxy services may require different servers for

each service. Proxy services usually require modifications to

clients, procedures, or both. Proxy services aren’t workable for some services. Proxy services don’t protect you from all protocol

weaknesses.


Proxying without a Proxy Server

Store-and-Forward services naturally support proxying.

Examples:– E-mail (SMTP).– News (NNTP).– Time (NTP).


Internet Resources on Security Issues


WWW Pages

http://www.telstra.com.au/info/security.html http://www.cs.purdue.edu/coast/coast.html


Mailing Lists

[email protected]– ftp://ftp.greatcircle.com/pub/firewalls/– http://www.greatcircle.com/firewalls/

[email protected] [email protected]

– ftp://net.tamu.edu/pub/security/lists/academic-firewalls

[email protected]


Newsgroups comp.security.announce. comp.security.unix. comp.security.misc. comp.security.firewalls. alt.security. comp.admin.policy. comp.protocols.tcp-ip. comp.unix.admin. comp.unix.wizards


Summary

In these dangerous times, firewalls are the best way to keep your site secure.

Although you’ve got to include other tipes of security in the mix, if you’re serious about connecting to the Internet, firewall should be at the very center of your security plans.

Documents

Computer Network Research Group ITB Security Issues Onno W. Purbo Computer Network Research Group Institute of Technology Bandung [email protected]