Fortinet Network Device IPS Manuale utente

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FortiGate

IPS User Guide

Version 3.0 MR7

USER GUIDE

FortiGate IPS User Guide

Version 3.0 MR7

September 16, 2008

01-30007-0080-20080916

publication including text, examples, diagrams or illustrations may be

reproduced, transmitted, or translated in any form or by any means,

electronic, mechanical, manual, optical or otherwise, for any purpose,

without prior written permission of Fortinet, Inc.

Trademarks

Dynamic Threat Prevention System (DTPS), APSecure, FortiASIC,

FortiBIOS, FortiBridge, FortiClient, FortiGate, FortiGate Unified Threat

Management System, FortiGuard, FortiGuard-Antispam, FortiGuard-

Antivirus, FortiGuard-Intrusion, FortiGuard-Web, FortiLog, FortiAnalyzer,

FortiManager, Fortinet, FortiOS, FortiPartner, FortiProtect, FortiReporter,

FortiResponse, FortiShield, FortiVoIP, and FortiWiFi are trademarks of

Fortinet, Inc. in the United States and/or other countries. The names of

actual companies and products mentioned herein may be the trademarks

of their respective owners.

Contents

FortiGate IPS User Guide Version 3.0 MR7

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Contents

Introduction ........................................................................................ 5

The FortiGate IPS............................................................................................... 5

About this document......................................................................................... 6

Document conventions.................................................................................. 6

Fortinet documentation .................................................................................... 6

Fortinet Knowledge Center .......................................................................... 8

Comments on Fortinet technical documentation .......................................... 8

Customer service and technical support ........................................................ 8

IPS overview and general configuration.......................................... 9

The FortiGate IPS............................................................................................... 9

IPS settings and controls .............................................................................. 9

When to use IPS ......................................................................................... 10

Network performance...................................................................................... 10

Default signature and anomaly settings ...................................................... 10

Default fail open setting............................................................................... 10

Controlling sessions .................................................................................... 11

Setting the buffer size ................................................................................. 11

Monitoring the network and dealing with attacks ........................................ 11

Configuring logging and alert email............................................................. 11

Attack log messages ................................................................................... 12

The FortiGuard Center ................................................................................ 13

Using IPS sensors in a protection profile ..................................................... 14

Creating a protection profile that uses IPS sensors .................................... 14

Adding protection profiles to firewall policies .............................................. 14

Adding protection profiles to user groups.................................................... 15

Predefined signatures ..................................................................... 17

IPS predefined signatures .............................................................................. 17

Viewing the predefined signature list ............................................................ 17

Fine tuning IPS predefined signatures for enhanced system performance 18

Custom signatures........................................................................... 21

IPS custom signatures.................................................................................... 21

Viewing the custom signature list.................................................................. 21

Custom signature configuration .................................................................... 22

Adding custom signatures using the web-based manager ......................... 22

Adding custom signatures using the CLI..................................................... 22

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Creating custom signatures........................................................................... 23

Custom signature fields .............................................................................. 23

Custom signature syntax ............................................................................ 24

Example custom signatures........................................................................ 33

Protocol decoders ........................................................................... 37

Protocol decoders........................................................................................... 37

Upgrading the IPS protocol decoder list....................................................... 37

Viewing the protocol decoder list.................................................................. 38

IPS sensors ...................................................................................... 39

Viewing the IPS sensor list............................................................................. 39

Adding an IPS sensor ................................................................................. 40

Configuring IPS sensors................................................................................. 40

Configuring filters ........................................................................................ 42

Configuring pre-defined and custom overrides ........................................... 43

DoS sensors..................................................................................... 45

Viewing the DoS sensor list ........................................................................... 46

Configuring DoS sensors ............................................................................... 46

Understanding the anomalies ........................................................................ 48

SYN flood attacks ............................................................................ 51

What is a SYN flood attack? ........................................................................... 51

How SYN floods work ..................................................................................... 51

The FortiGate IPS Response to SYN flood attacks ...................................... 52

What is SYN threshold?.............................................................................. 52

What is SYN proxy? ................................................................................... 52

How IPS works to prevent SYN floods........................................................ 52

Configuring SYN flood protection ................................................................. 54

Suggested settings for different network conditions .................................. 54

ICMP sweep attacks......................................................................... 55

What is an ICMP sweep? ................................................................................ 55

How ICMP sweep attacks work ...................................................................... 55

The FortiGate IPS response to ICMP sweep attacks.................................... 55

Predefined ICMP signatures ....................................................................... 56

ICMP sweep anomalies .............................................................................. 57

Configuring ICMP sweep protection.............................................................. 58

Suggested settings for different network conditions .................................. 58

Index.................................................................................................. 59

Introduction The FortiGate IPS

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Introduction

This section introduces you to the FortiGate Intrusion Prevention System (IPS)

and the following topics:

•The FortiGate IPS

•About this document

•Fortinet documentation

•Customer service and technical support

The FortiGate IPS

Spam and viruses are not the only threats facing enterprises and small

businesses. Sophisticated, automated attack tools are prevalent on the Internet

today, making intrusion detection and prevention vital to securing corporate

networks. An attack or intrusion can be launched to steal confidential information,

force a costly web site crash, or use network resources to launch other attacks.

The FortiGate IPS detects intrusions by using attack signatures for known

intrusion methods, and detects anomalies in network traffic to identify new or

unknown intrusions. Not only can the IPS detect and log attacks, but users can

choose actions to take on the session when an attack is detected. This guide

describes how to configure and use the IPS and the IPS response to some

common attacks.

This guide describes:

•IPS overview and general configuration

•Predefined signatures

•Custom signatures

•Protocol decoders

•IPS sensors

•DoS sensors

•SYN flood attacks

•ICMP sweep attacks

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About this document Introduction

About this document

Document conventions

The following document conventions are used in this guide:

• In the examples, private IP addresses are used for both private and public IP

addresses.

• Notes and Cautions are used to provide important information:

Typographic conventions

FortiGate documentation uses the following typographical conventions:

Fortinet documentation

The most up-to-date publications and previous releases of Fortinet™ product

documentation are available from the Fortinet Technical Documentation web site

at http://docs.forticare.com.

The following FortiGate product documentation is available:

• FortiGate QuickStart Guide

Provides basic information about connecting and installing a FortiGate unit.

Note: Highlights useful additional information.

Caution: Warns you about commands or procedures that could have unexpected or

undesirable results including loss of data or damage to equipment.

Convention Example

Keyboard input In the Gateway Name field, type a name for the remote VPN

peer or client (for example, Central_Office_1).

Code examples F-SBID (--protocol tcp; --flow

established; --content "content here";

--no_case)

CLI command syntax config firewall policy

edit id_integer

set http_retry_count <retry_integer>

set natip <address_ipv4mask>

end

Document names FortiGate Administration Guide

File content <HTML><HEAD><TITLE>Firewall

Authentication</TITLE></HEAD>

<BODY><H4>You must authenticate to use this

service.</H4>

Menu commands Go to VPN > IPSEC > Phase 1 and select Create New.

Program output Welcome!

Variables <address_ipv4>

Introduction Fortinet documentation

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• FortiGate Installation Guide

Describes how to install a FortiGate unit. Includes a hardware reference,

default configuration information, installation procedures, connection

procedures, and basic configuration procedures. Choose the guide for your

product model number.

• FortiGate Administration Guide

Provides basic information about how to configure a FortiGate unit, including

how to define FortiGate protection profiles and firewall policies; how to apply

intrusion prevention, antivirus protection, web content filtering, and spam

filtering; and how to configure a VPN.

• FortiGate online help

Provides a context-sensitive and searchable version of the Administration

Guide in HTML format. You can access online help from the web-based

manager as you work.

• FortiGate CLI Reference

Describes how to use the FortiGate CLI and contains a reference to all

FortiGate CLI commands.

• FortiGate Log Message Reference

Describes the structure of FortiGate log messages and provides information

about the log messages that are generated by FortiGate units.

• FortiGate High Availability User Guide

Contains in-depth information about the FortiGate high availability feature and

the FortiGate clustering protocol.

• FortiGate IPS User Guide

Describes how to configure the FortiGate Intrusion Prevention System settings

and how the FortiGate IPS deals with some common attacks.

• FortiGate IPSec VPN User Guide

Provides step-by-step instructions for configuring IPSec VPNs using the web-

based manager.

• FortiGate SSL VPN User Guide

Compares FortiGate IPSec VPN and FortiGate SSL VPN technology, and

describes how to configure web-only mode and tunnel-mode SSL VPN access

for remote users through the web-based manager.

• FortiGate PPTP VPN User Guide

Explains how to configure a PPTP VPN using the web-based manager.

• FortiGate Certificate Management Guide

Contains procedures for managing digital certificates including generating

certificate requests, installing signed certificates, importing CA root certificates

and certificate revocation lists, and backing up and restoring installed

certificates and private keys.

• FortiGate VLANs and VDOMs User Guide

Describes how to configure VLANs and VDOMS in both NAT/Route and

Transparent mode. Includes detailed examples.

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Customer service and technical support Introduction

Fortinet Knowledge Center

Additional Fortinet technical documentation is available from the Fortinet

Knowledge Center. The knowledge center contains troubleshooting and how-to

articles, FAQs, technical notes, and more. Visit the Fortinet Knowledge Center at

http://kc.forticare.com.

Comments on Fortinet technical documentation

Please send information about any errors or omissions in this document, or any

Fortinet technical documentation, to [email protected].

Customer service and technical support

Fortinet Technical Support provides services designed to make sure that your

Fortinet systems install quickly, configure easily, and operate reliably in your

network.

Please visit the Fortinet Technical Support web site at http://support.fortinet.com

to learn about the technical support services that Fortinet provides.

IPS overview and general configuration The FortiGate IPS

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IPS overview and general

configuration

This section contains the following topics:

•The FortiGate IPS

•Network performance

•Monitoring the network and dealing with attacks

•Using IPS sensors in a protection profile

The FortiGate IPS

An IPS is an Intrusion Prevention System for networks. While early systems

focused on intrusion detection, the continuing rapid growth of the Internet, and the

potential for the theft of sensitive data, has resulted in the need for not only

detection, but prevention.

The FortiGate IPS detects intrusions by using attack signatures for known

intrusion methods, and detects anomalies in network traffic to identify new or

unknown intrusions. Not only can the IPS detect and log attacks, but users can

choose actions to take on the session when an attack is detected. This guide

describes how to configure and use the IPS and the IPS response to some

common attacks.

Both the IPS predefined signatures and the IPS engine are upgraded through the

FortiGuard Distribution Network (FDN). These upgrades provide the latest

protection against IM/P2P and other threats. Firmware upgrades will update

anomaly options. The FortiGate IPS default settings implement the recommended

settings for all signatures and anomalies. Signature settings and some anomaly

thresholds are pre-set to work best with the normal traffic on the protected

networks. You can create custom signatures for the FortiGate IPS in diverse

network environments.

Administrators are notified of intrusions and possible intrusions through log

messages and alert email.

Packet logging provides administrators with the ability to analyze packets for

forensics and false positive detection.

IPS settings and controls

Configure the Intrusion Protection system using either the web-based manager or

the CLI, then select IPS sensors in individual firewall protection profiles.

Note: If virtual domains are enabled on the FortiGate unit, the Intrusion Protection settings

are configured separately in each VDOM. All sensors and custom signatures will appear

only in the VDOM in which they were created.

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Network performance IPS overview and general configuration

To create an IPS sensor, go to Intrusion Protection > IPS Sensor. See “IPS

sensors” on page 39 for details. To access the protection profile IPS sensor

selection, go to Firewall > Protection Profile, select Edit or Create New, and

select IPS.

To create a DoS Sensor, go to Intrusion Protection > DoS Sensor. See “DoS

sensors” on page 45 for details.

When to use IPS

IPS is best for large networks or for networks protecting highly sensitive

information. Using IPS effectively requires monitoring and analysis of the attack

logs to determine the nature and threat level of an attack. An administrator can

adjust the threshold levels to ensure a balance between performance and

intrusion prevention. Small businesses and home offices without network

administrators may be overrun with attack log messages and not have the

networking background required to configure the thresholds and other IPS

settings. In addition, the other protection features in the FortiGate unit, such as

antivirus (including grayware), spam filters, and web filters offer excellent

protection for all networks.

Network performance

The FortiGate IPS is extremely accurate and reliable as an in-line network device.

Independent testing shows that the FortiGate IPS successfully detects and blocks

attacks even under high traffic loads, while keeping latency within expected limits.

This section describes:

•Default signature and anomaly settings

•Default fail open setting

•Controlling sessions

•Setting the buffer size

Default signature and anomaly settings

You can use IPS sensors to apply appropriate IPS signatures to different

protection profiles, then different firewall policies.

Default fail open setting

If for any reason the IPS should cease to function, it will fail open by default. This

means that crucial network traffic will not be blocked and the Firewall will continue

to operate while the problem is resolved.

Change the default fail open setting using the CLI:

config ips global

set fail-open [enable | disable]

end

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