Firewalls & Intrusion Detection Systems

Firewalls &

Intrusion Detection Systems

Communications, Networking & Computer Security

Sanjay Goel University at Albany

• Firewall– Definition– Types– Configuration– Lab Exercise (Kerio Personal Firewall)

• IDS– Definition– Operation– Lab Exercises

Outline

• A firewall is any device used to prevent outsiders from gaining access to your network.

• It checks each packet against a list of rules to permit or deny its transmission

• Firewalls commonly implement exclusionary schemes or rules that sort out wanted and unwanted addresses.– They filter all traffic between a protected (“inside”)

network and a less trustworthy (“outside”) network

Firewall What is a Firewall?

• Firewalls can be composed of software, hardware, or, most commonly, both. – The software components can be

either proprietary, shareware, or freeware.

– The hardware is typically any hardware that supports the firewall software.

Firewall Composition?

• All traffic in both direction must pass through the firewall

• Only authorized traffic should be allowed to pass

• Firewall should itself be immune to penetration– Compromised firewall can completely undermine

the network security

• Tradeoff between security and productivity– Internal network could be completely secure, but

employees may not be able to communicate

Firewall Design Goals

• There are different kinds of firewalls, and each type has its advantages & disadvantages.

• Firewalls can be classified in two broad categories– Network Level Firewalls– Personal Firewalls

Firewall Types

• Network-level firewalls are usually router based. – Rules of who & what can access your network is applied

at router level.

• Scheme is applied through a technique called packet filtering

• Network Level Firewalls can be classified as– Packet-Filtering Firewalls

• The simplest and most effective type of firewalls

– Stateful Inspection Firewalls• Maintain state info from a packet to another in the

input stream

– Application-Level Firewalls (Proxies)• Proxy server, a relay of application-level traffic

Firewall Network Level Firewalls

• Packet Filtering is the process of examining the packets that come to the router from the outside world.

• Packet headers are inspected by a firewall or router to make a decision to block the packet or allow access

• Two Approaches:– Stateless (a.k.a. static)– Stateful

Firewall Packet Filtering

Sanjay Goel, School of Business

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• Ignores the “state” of the connection• Each packet header is examined

individually and compared to a “rule base”– Packet data is ignored

• Common criteria to filter on:– Protocol Type– IP address– Port Number– Message Type

Firewall Stateless Packet Filtering


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• Maintains a record of the state of the connection (referred to as state table)

• Packet is compared against both rule base and state table

• Some stateful filters can examine both packet header and content

• Called “stateful” because it permits outgoing sessions while denying incoming sessions

Firewall Stateful Packet Filtering

• When a remote user contacts a network running an application gateway, the gateway blocks the remote connection.

• Instead of passing the connection along, the gateway examines various fields in the request.

• If these meet a set of predefined rules, the gateway creates a bridge between the remote host and the internal host.

Firewall Application Gateway Firewall

• A list of rules describing which packets are to be forwarded

• Each packet is compared against this list

• The longer the list the greater the latency (delay)

• Examples:– From any to any port 80 permit– From any to any PORT any deny– From *.albany.edu to any PORT any DENY

Firewall Access Policy


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• Firewalls are not a complete solution to all computer security problems, limitations:– The firewall cannot protect against

attacks that bypass the firewall– The firewall does not protect against

internal threats– The firewall cannot protect against the

transfer of virus-infected programs or files

Firewall Limitations


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Firewall Configuration Strategies

Screening Router

• Simple

• Filters traffic to internal computers

• Provides minimal security

Internet

Router

External Interface10.1.1.200 /24

Internal Interface192.168.2.1 /24

192.168.2.2 192.168.2.3 192.168.2.4 192.168.2.5 192.168.2.6

Source: Guide To Firewalls and Network Security


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Internet

Router

192.168.2.2 192.168.2.3 192.168.2.4 192.168.2.5 192.168.2.6

ApplicationGateway

Screening Host

• Host makes Internet request

• Gateway receives client request and makes a request on behalf of the client

• Host IP address never displayed to public



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Two Routers, One Firewall

• External router can perform initial static packet filtering

• Internal router can perform stateful packet filtering

• Multiple internal routers can direct traffic to different subnets

Internet

Router

192.168.2.2 192.168.2.3 192.168.2.4 192.168.2.5 192.168.2.6

Router

Firewall

LAN Gateway



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DMZ Screened Subnet

• DMZ sits outside internal network but is connected to the firewall

• Public can access servers residing in DMZ, but cannot connect to internal LAN

Internet

Router

192.168.2.2 192.168.2.3 192.168.2.4 192.168.2.5 192.168.2.6

Router

Firewall

LAN Gateway

DMZ

Web Server Email Server FTP Server

10.1.1.2 10.1.1.3 10.1.1.4

10.1.1.1 /24

192.168.1.1 /24



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Two Firewalls, One DMZ

• First firewall controls traffic between the Internet and DMZ

• Second firewall controls traffic between the internal network and DMZ

• Second firewall can also be a failover firewall

Internet

192.168.2.2 192.168.2.3 192.168.2.4 192.168.2.5 192.168.2.6

Router

Firewall

LAN Gateway

DMZ

Web Server Email Server FTP Server

10.1.1.2 10.1.1.3 10.1.1.4

10.1.1.1 /24

192.168.1.1 /24

Router

• What’s KPF? A software agent builds a barrier between PC and the

Internet, to protect PC against hacker attacks and data leaks.

• Why KPF?– KPF is designed to protect PC against attacks from both

the Internet, and other computers in the local network.

– KPF controls all data flow in both directions – from the Internet to your computer and vice versa

– KPF can block all attempted communication allowing only what you choose to permit.

Firewall Kerio Personal Firewall (KPF)


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Lab Exercise

Configure Kerio Personal Firewall

KPF How does it work?

• Blocks all externally originated IP traffic

• Three security settings for easy configuration

• MD5 signature verification protects the computer from Trojan horses

• Protecting from Denial of Service (DOS) attacks to applications or services

• Connections dialog clearly displays each application's activity at any given moment

KPF Features

• Availability (KPF version 4.1.3):

– Available for trial for home use (limited free version) http://www.kerio.com/kpf_download.html

– Manual is available at the following site http://download.kerio.com/dwn/kpf/kpf41-en-v3.pdf

– Business and institutional customers are encouraged to download this software for evaluation purposes.

• Platform:– For Windows 98, Me, NT, 2000 and XP

– (Win 95 not available any more)

KPF Features Cont’d.

• System requirements:• CPU Intel Pentium or 100% compatible • 64 MB RAM • 8 MB hard drive space (for installation only; at least

10 MB of additional space is recommended for logging)

• Installation: • Executing the installation archive (kerio-pf-201-en-

win.exe)

• Choose the directory KPF be installed, or leave the default setting (C:\Program Files\Kerio\Personal Firewall)

• Restart system after installation in order for the low-lever driver to be loaded

KPF Installation

• Overview — list of active and open ports, statistics, user preferences.

• Network Security — rules for network communication of individual applications, Packet filtering, trusted area definitions

• System Security — rules for startup of individual applications• Intrusions — configuration of parameters which will be used

for detection of known intrusion types• Web - web content rules (URL filter, pop-ups blocking, control

over sent data)• Logs & Alters -- logs viewing and settings

KPF Configuration

• The Firewall Engine takes care of all KPF functions

• It runs as a background application

• It is represented by an icon in the System Tray

• Right click the icon:

– Stop All Traffic

– Firewall Status

– Administration

KPF Firewall Engine

KPF Configuration Window

Test

KPF Administration

KPF Status Window

• Level of Security: (KPF allows 3 security levels)

– Permit Unknown: minimum security

– Ask Me First: all communication is denied implicitly at this level

– Deny Unknown: all communication is denied which is not explicitly permitted by the existing filter rules

KPF Security Settings

• Test

KPF Security Settings Cont’d.

KPF Interaction with Users (Incoming)

KPF Interaction with Users (Outgoing)

Comments

KPF Packet Filtering Rules

KPF Application MD5 Signature

• The filter.log file is used for logging KPF actions on a local computer

• Filter.log is a text file where each record is placed on a new line. It has the following format: – 1,[08/Jun/2001 16:52:09] Rule 'Internet

Information Services': Blocked: In TCP, richard.kerio.cz [192.168.2.38:3772]->localhost:25, Owner: G:\WINNT\SYSTEM32\INETSRV\INETINFO.EXE

• How to read this log file?

KPF Filter.log File


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Intrusion Detection Systems

• An intrusion detection system (IDS) monitors systems and analyzes network traffic to detect signs of intrusion.

• An IDS can detect a variety of attacks in progress as well as well as attempts to scan a network for weaknesses.

• An IDS can be a dedicated network appliance or a software solution installed on a host computer.

• Two kinds of IDS Systems– Client Based (On a single node)– Network Based (Protecting the entire network)

IDS What Does it Do?

• If configured correctly, a network intrusion detection system (NIDS) can monitor all traffic on a network segment.

• A NIDS is most effective when used in conjunction with a firewall solution, and having all of its dependent components being properly connected and functioning.

IDS How does it work?


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• NIDS can be installed on the external routers, the internal routers, or both.

• Placing NIDS on external routers enables detection of attacks from the Internet

• Placing NIDS on internal routers enables detection of internal hosts attempting to access the Internet on suspicious ports.

IDS Configuration

• A NIDS/IDS mainly use anomaly or pattern detection to identify an intrusion or intrusion attempt.

• An anomaly example: This involves monitoring resource use, network traffic, user behavior and comparing it against normal levels.

• If a user that normally only accesses the system between 9 am – 5pm, suddenly logs on at 3 am then this may indicate that an intruder has compromised the user’s account. A NIDS/IDS would then alert administrators to this suspicious activity.

• A NIDS/IDS can detect hacker attempts to scan your network for intelligence gathering purposes.

IDS Methods of Detection

• Sits On Network location and “checks” packets that travel across the network.

• If a packet contains a certain “footprint”, then it triggers an alert

• Audit logs are generated and kept as records of alerts.

IDS Network Packet Checking

• ISS Internet Security Systems (Black Ice Guardian)– Used by individuals and small business

networks.

– Looks for common algorithms concealed or “wrapped” in wrappers i.e. TCP Wrapper.

– Can be configured as an IDS and a Firewall.

– Can track unauthorized traffic and block the ports the intruding script/software is using.

IDS Commonly Used IDS Systems (Windows)

• Axent: Raptor v6.5• Checkpoint: FW1 v4.1• Cisco: PIX v525• MS: Proxy v2.0

IDS Vendor Firewalls & Versions (Hardware Based)

Zone Alarm Pro!

View Demo

http://download.zonelabs.com/bin/media/flash/zap31demo/final083002_01.swf

• Edward Zhang• Michael LaBarge• Christopher Brown

Firewalls & IDSContributors

Documents

Firewalls & Intrusion Detection Systems