6.3. Web Content Filtering
6.3.1. Overview
Web traffic is one of the biggest sources for security issues and misuse of the Internet. Inappropriate
surfing habits can expose a network to many security threats as well as legal and regulatory
liabilities. Productivity and Internet bandwidth can also be impaired.
Filtering Mechanisms
Through the HTTP ALG, NetDefendOS provides the following mechanisms for filtering out web
content that is deemed inappropriate for an organization or group of users:
•
Active Content Handling can be used to remove content from web pages that the administrator
considers a potential threat, such as ActiveX objects and Java Applets.
•
Static Content Filtering provides a means for manually classifying web sites as "good" or "bad".
This is also known as URL blacklisting and whitelisting.
•
Dynamic Content Filtering is a powerful feature that enables the administrator to allow or block
access to web sites depending on the category they have been classified into by an automatic
classification service. Dynamic content filtering requires a minimum of administration effort and
has very high accuracy.
Note: WCF is enabled through the HTTP ALG
All Web Content Filtering is enabled via the HTTP ALG which is described in
Section 6.2.2, “The HTTP ALG”.
6.3.2. Active Content Handling
Some web content can contain malicious code designed to harm the workstation or the network
from where the user is surfing. Typically, such code is embedded into various types of objects or
files which are embedded into web pages.
NetDefendOS includes support for removing the following types of objects from web page content:
•
ActiveX objects (including Flash)
•
Java applets
•
Javascript/VBScript code
•
Cookies
•
Invalidly formatted UTF-8 Characters (invalid URL formatting can be used to attack
webservers)
The object types to be removed can be selected individually by configuring the corresponding HTTP
Application Layer Gateway accordingly.
Caution: Consider the consequences of removing objects
Careful consideration should be given before enabling removal any object types from
web content. Many web sites use Javascript and other types of client-side code and in
most cases, the code is non-malicious. Common examples of this is the scripting used
to implement drop-down menus as well as hiding and showing elements on web pages.
6.3. Web Content Filtering
Chapter 6. Security Mechanisms
325
Summary of Contents for NetDefend DFL-1660
Page 28: ...1 3 NetDefendOS State Engine Packet Flow Chapter 1 NetDefendOS Overview 28 ...
Page 88: ...2 6 3 Restore to Factory Defaults Chapter 2 Management and Maintenance 88 ...
Page 166: ...3 10 DNS Chapter 3 Fundamentals 166 ...
Page 254: ...4 7 5 Advanced Settings for Transparent Mode Chapter 4 Routing 254 ...
Page 268: ...5 4 IP Pools Chapter 5 DHCP Services 268 ...
Page 368: ...6 7 Blacklisting Hosts and Networks Chapter 6 Security Mechanisms 368 ...
Page 390: ...7 4 7 SAT and FwdFast Rules Chapter 7 Address Translation 390 ...
Page 414: ...8 3 Customizing Authentication HTML Pages Chapter 8 User Authentication 414 ...
Page 490: ...9 8 6 Specific Symptoms Chapter 9 VPN 490 ...
Page 528: ...10 4 6 Setting Up SLB_SAT Rules Chapter 10 Traffic Management 528 ...
Page 544: ...11 7 HA Advanced Settings Chapter 11 High Availability 544 ...
Page 551: ...12 3 5 Limitations Chapter 12 ZoneDefense 551 ...
Page 574: ...Default 512 13 9 Miscellaneous Settings Chapter 13 Advanced Settings 574 ...
Page 575: ...13 9 Miscellaneous Settings Chapter 13 Advanced Settings 575 ...